docs: enable syntax highlighting in several docs files

... for better readability

Closes #6286

docs/CODE_STYLE.md

@@ -36,18 +36,22 @@ library-global symbols.
 We use only spaces for indentation, never TABs. We use two spaces for each new
 open brace.
 
+```c
 if(something_is_true) {
   while(second_statement == fine) {
     moo();
   }
 }
+```
 
 ## Comments
 
 Since we write C89 code, **//** comments are not allowed. They weren't
 introduced in the C standard until C99. We use only **/* comments */**.
 
+```c
 /* this is a comment */
+```
 
 ## Long lines
 
@@ -69,42 +73,52 @@ In if/while/do/for expressions, we write the open brace on the same line as
 the keyword and we then set the closing brace on the same indentation level as
 the initial keyword. Like this:
 
+```c
 if(age < 40) {
   /* clearly a youngster */
 }
+```
 
 You may omit the braces if they would contain only a one-line statement:
 
+```c
 if(!x)
   continue;
+```
 
 For functions the opening brace should be on a separate line:
 
+```c
 int main(int argc, char **argv)
 {
   return 1;
 }
+```
 
 ## 'else' on the following line
 
 When adding an **else** clause to a conditional expression using braces, we
 add it on a new line after the closing brace. Like this:
 
+```c
 if(age < 40) {
   /* clearly a youngster */
 }
 else {
   /* probably grumpy */
 }
+```
 
 ## No space before parentheses
 
 When writing expressions using if/while/do/for, there shall be no space
 between the keyword and the open parenthesis. Like this:
 
+```c
 while(1) {
   /* loop forever */
 }
+```
 
 ## Use boolean conditions
 
@@ -112,40 +126,50 @@ Rather than test a conditional value such as a bool against TRUE or FALSE, a
 pointer against NULL or != NULL and an int against zero or not zero in
 if/while conditions we prefer:
 
+```c
 result = do_something();
 if(!result) {
   /* something went wrong */
   return result;
 }
+```
 
 ## No assignments in conditions
 
 To increase readability and reduce complexity of conditionals, we avoid
 assigning variables within if/while conditions. We frown upon this style:
 
+```c
 if((ptr = malloc(100)) == NULL)
   return NULL;
+```
 
 and instead we encourage the above version to be spelled out more clearly:
 
+```c
 ptr = malloc(100);
 if(!ptr)
   return NULL;
+```
 
 ## New block on a new line
 
 We never write multiple statements on the same source line, even for very
 short if() conditions.
 
+```c
 if(a)
   return TRUE;
 else if(b)
   return FALSE;
+```
 
 and NEVER:
 
+```c
 if(a) return TRUE;
 else if(b) return FALSE;
+```
 
 ## Space around operators
 
@@ -155,6 +179,7 @@ have no space.
 
 Examples:
 
+```c
 bla = func();
 who = name[0];
 age += 1;
@@ -166,22 +191,27 @@ Examples:
 contents = *pointer;
 complement = ~bits;
 empty = (!*string) ? TRUE : FALSE;
+```
 
 ## No parentheses for return values
 
 We use the 'return' statement without extra parentheses around the value:
 
+```c
 int works(void)
 {
   return TRUE;
 }
+```
 
 ## Parentheses for sizeof arguments
 
 When using the sizeof operator in code, we prefer it to be written with
 parentheses around its argument:
 
+```c
 int size = sizeof(int);
+```
 
 ## Column alignment
 
@@ -195,32 +225,40 @@ the statement it is. Operators should not start continuation lines. In other
 cases follow the 2-space indent guideline. Here are some examples from
 libcurl:
 
+```c
 if(Curl_pipeline_wanted(handle->multi, CURLPIPE_HTTP1) &&
    (handle->set.httpversion != CURL_HTTP_VERSION_1_0) &&
    (handle->set.httpreq == HTTPREQ_GET ||
     handle->set.httpreq == HTTPREQ_HEAD))
   /* didn't ask for HTTP/1.0 and a GET or HEAD */
   return TRUE;
+```
 
 If no parenthesis, use the default indent:
 
+```c
 data->set.http_disable_hostname_check_before_authentication =
   (0 != va_arg(param, long)) ? TRUE : FALSE;
+```
 
 Function invoke with an open parenthesis:
 
+```c
 if(option) {
   result = parse_login_details(option, strlen(option),
                                (userp ? &user : NULL),
                                (passwdp ? &passwd : NULL),
                                NULL);
 }
+```
 
 Align with the "current open" parenthesis:
 
+```c
 DEBUGF(infof(data, "Curl_pp_readresp_ %d bytes of trailing "
              "server response left\n",
              (int)clipamount));
+```
 
 ## Platform dependent code
 
@@ -234,6 +272,7 @@ to constants when libcurl is built without that feature, to make the code
 seamless. Like this example where the **magic()** function works differently
 depending on a build-time conditional:
 
+```c
 #ifdef HAVE_MAGIC
 void magic(int a)
 {
@@ -244,22 +283,27 @@ depending on a build-time conditional:
 #endif
 
 int content = magic(3);
+```
 
 ## No typedefed structs
 
 Use structs by all means, but do not typedef them. Use the `struct name` way
 of identifying them:
 
+```c
 struct something {
    void *valid;
    size_t way_to_write;
 };
 struct something instance;
+```
 
 **Not okay**:
 
+```c
 typedef struct {
    void *wrong;
    size_t way_to_write;
 } something;
 something instance;
+```

docs/DYNBUF.md

@@ -11,7 +11,9 @@ without using the dedicated dynbuf API.
 
 ## init
 
+```c
 void Curl_dyn_init(struct dynbuf *s, size_t toobig);
+```
 
 This inits a struct to use for dynbuf and it can't fail. The `toobig` value
 **must** be set to the maximum size we allow this buffer instance to grow to.
@@ -19,44 +21,58 @@ The functions below will return `CURLE_OUT_OF_MEMORY` when hitting this limit.
 
 ## free
 
+```c
 void Curl_dyn_free(struct dynbuf *s);
+```
 
 Free the associated memory and clean up. After a free, the `dynbuf` struct can
 be re-used to start appending new data to.
 
 ## addn
 
+```c
 CURLcode Curl_dyn_addn(struct dynbuf *s, const void *mem, size_t len);
+```
 
 Append arbitrary data of a given length to the end of the buffer.
 
 ## add
 
+```c
 CURLcode Curl_dyn_add(struct dynbuf *s, const char *str);
+```
 
 Append a C string to the end of the buffer.
 
 ## addf
 
+```c
 CURLcode Curl_dyn_addf(struct dynbuf *s, const char *fmt, ...);
+```
 
 Append a `printf()`-style string to the end of the buffer.
 
 ## vaddf
 
+```c
 CURLcode Curl_dyn_vaddf(struct dynbuf *s, const char *fmt, va_list ap);
+```
 
 Append a `vprintf()`-style string to the end of the buffer.
 
 ## reset
 
+```c
 void Curl_dyn_reset(struct dynbuf *s);
+```
 
 Reset the buffer length, but leave the allocation.
 
 ## tail
 
-    CURLcode Curl_dyn_tail(struct dynbuf *s, size_t length)
+```c
+CURLcode Curl_dyn_tail(struct dynbuf *s, size_t length);
+```
 
 Keep `length` bytes of the buffer tail (the last `length` bytes of the
 buffer). The rest of the buffer is dropped. The specified `length` must not be
@@ -64,7 +80,9 @@ larger than the buffer length.
 
 ## ptr
 
+```c
 char *Curl_dyn_ptr(const struct dynbuf *s);
+```
 
 Returns a `char *` to the buffer if it has a length, otherwise a NULL. Since
 the buffer may be reallocated, this pointer should not be trusted or used
@@ -72,7 +90,9 @@ anymore after the next buffer manipulation call.
 
 ## uptr
 
+```c
 unsigned char *Curl_dyn_uptr(const struct dynbuf *s);
+```
 
 Returns an `unsigned char *` to the buffer if it has a length, otherwise a
 NULL. Since the buffer may be reallocated, this pointer should not be trusted
@@ -80,7 +100,9 @@ or used anymore after the next buffer manipulation call.
 
 ## len
 
+```c
 size_t Curl_dyn_len(const struct dynbuf *s);
+```
 
 Returns the length of the buffer in bytes. Does not include the terminating
 zero byte.

docs/INSTALL.md

@@ -148,7 +148,9 @@ debug multithreaded dynamic C runtime.
 
 Make sure that MinGW32's bin dir is in the search path, for example:
 
+```cmd
 set PATH=c:\mingw32\bin;%PATH%
+```
 
 then run `mingw32-make mingw32` in the root dir. There are other
 make targets available to build libcurl with more features, use:
@@ -164,20 +166,26 @@ to verify that the provided `Makefile.m32` files use the proper paths, and
 adjust as necessary. It is also possible to override these paths with
 environment variables, for example:
 
+```cmd
 set ZLIB_PATH=c:\zlib-1.2.8
 set OPENSSL_PATH=c:\openssl-1.0.2c
 set LIBSSH2_PATH=c:\libssh2-1.6.0
+```
 
 It is also possible to build with other LDAP SDKs than MS LDAP; currently
 it is possible to build with native Win32 OpenLDAP, or with the Novell CLDAP
 SDK. If you want to use these you need to set these vars:
 
+```cmd
 set LDAP_SDK=c:\openldap
 set USE_LDAP_OPENLDAP=1
+```
 
 or for using the Novell SDK:
 
+```cmd
 set USE_LDAP_NOVELL=1
+```
 
 If you want to enable LDAPS support then set LDAPS=1.
 
@@ -280,9 +288,11 @@ the same curl binary is executed on older cats. For example, running these
 commands in curl's directory in the shell will build the code such that it
 will run on cats as old as OS X 10.6 ("Snow Leopard") (using bash):
 
+```bash
 export MACOSX_DEPLOYMENT_TARGET="10.6"
 ./configure --with-secure-transport
 make
+```
 
 # Android
 
@@ -295,6 +305,7 @@ where it has been installed and then set up some environment variables before
 launching `configure`. On macOS, those variables could look like this to compile
 for `aarch64` and API level 29:
 
+```bash
 export NDK=~/Library/Android/sdk/ndk/20.1.5948944
 export HOST_TAG=darwin-x86_64
 export TOOLCHAIN=$NDK/toolchains/llvm/prebuilt/$HOST_TAG
@@ -305,6 +316,7 @@ for `aarch64` and API level 29:
 export LD=$TOOLCHAIN/bin/aarch64-linux-android-ld
 export RANLIB=$TOOLCHAIN/bin/aarch64-linux-android-ranlib
 export STRIP=$TOOLCHAIN/bin/aarch64-linux-android-strip
+```
 
 When building on Linux or targeting other API levels or architectures, you need
 to adjust those variables accordingly. After that you can build curl like this:
@@ -337,6 +349,7 @@ configure with any options you need.  Be sure and specify the `--host` and
 example of cross-compiling for the IBM 405GP PowerPC processor using the
 toolchain from MonteVista for Hardhat Linux.
 
+```bash
 #! /bin/sh
 
 export PATH=$PATH:/opt/hardhat/devkit/ppc/405/bin
@@ -353,6 +366,7 @@ toolchain from MonteVista for Hardhat Linux.
     --build=i586-pc-linux-gnu
     --prefix=/opt/hardhat/devkit/ppc/405/target/usr/local
     --exec-prefix=/usr/local
+```
 
 You may also need to provide a parameter like `--with-random=/dev/urandom` to
 configure as it cannot detect the presence of a random number generating

docs/INTERNALS.md

@@ -773,7 +773,9 @@ Track Down Memory Leaks
 
   Add a line in your application code:
 
-       `curl_dbg_memdebug("dump");`
+```c
+  curl_dbg_memdebug("dump");
+```
 
   This will make the malloc debug system output a full trace of all resource
   using functions to the given file name. Make sure you rebuild your program

docs/MANUAL.md

@@ -307,12 +307,14 @@ Example:
 
 (page located at `http://www.formpost.com/getthis/`)
 
+```html
 <form action="post.cgi" method="post">
 <input name=user size=10>
 <input name=pass type=password size=10>
 <input name=id type=hidden value="blablabla">
 <input name=ding value="submit">
 </form>
+```
 
 We want to enter user 'foobar' with password '12345'.
 
@@ -419,7 +421,9 @@ if it should be used on secure connections only (`secure`).
 
 If you've received a page from a server that contains a header like:
 
+```http
 Set-Cookie: sessionid=boo123; path="/foo";
+```
 
 it means the server wants that first pair passed on when we get anything in a
 path beginning with "/foo".

docs/TheArtOfHttpScripting.md

@@ -222,10 +222,12 @@
 
  A GET-form uses the method GET, as specified in HTML like:
 
+```html
 <form method="GET" action="junk.cgi">
   <input type=text name="birthyear">
   <input type=submit name=press value="OK">
 </form>
+```
 
  In your favorite browser, this form will appear with a text box to fill in
  and a press-button labeled "OK". If you fill in '1905' and press the OK
@@ -258,10 +260,12 @@
 
  The form would look very similar to the previous one:
 
+```html
 <form method="POST" action="junk.cgi">
   <input type=text name="birthyear">
   <input type=submit name=press value=" OK ">
 </form>
+```
 
  And to use curl to post this form with the same data filled in as before, we
  could do it like:
@@ -293,10 +297,12 @@
  This method is mainly designed to better support file uploads. A form that
  allows a user to upload a file could be written like this in HTML:
 
+```html
 <form method="POST" enctype='multipart/form-data' action="upload.cgi">
   <input type=file name=upload>
   <input type=submit name=press value="OK">
 </form>
+```
 
  This clearly shows that the Content-Type about to be sent is
  `multipart/form-data`.
@@ -315,11 +321,13 @@
  A similar example form with one visible field, one hidden field and one
  submit button could look like:
 
+```html
 <form method="POST" action="foobar.cgi">
   <input type=text name="birthyear">
   <input type=hidden name="person" value="daniel">
   <input type=submit name="press" value="OK">
 </form>
+```
 
  To POST this with curl, you won't have to think about if the fields are
  hidden or not. To curl they're all the same:

docs/VERSIONS.md

@@ -41,7 +41,9 @@ Version Numbers and Releases
  numbering scheme that can be used for comparison. The version number is
  defined as:
 
+```c
 #define LIBCURL_VERSION_NUM 0xXXYYZZ
+```
 
  Where XX, YY and ZZ are the main version, release and patch numbers in
  hexadecimal. All three number fields are always represented using two digits