docs/ALTSVC: remove what works and the experimental explanation

Also, put the TODO items at the bottom.

Closes #4198

docs/ALTSVC.md

@@ -2,21 +2,6 @@
 
 curl features **EXPERIMENTAL** support for the Alt-Svc: HTTP header.
 
-## Experimental
-
-Experimental support in curl means:
-
-1. Experimental features are provided to allow users to try them out and
-   provide feedback on functionality and API etc before they ship and get
-   "carved in stone".
-2. You must enable the feature when invoking configure as otherwise curl will
-   not be built with the feature present.
-3. We strongly advice against using this feature in production.
-4. **We reserve the right to change behavior** of the feature without sticking
-   to our API/ABI rules as we do for regular features, as long as it is marked
-   experimental.
-5. Experimental features are clearly marked so in documentation. Beware.
-
 ## Enable Alt-Svc in build
 
 `./configure --enable-alt-svc`
@@ -25,39 +10,6 @@ Experimental support in curl means:
 
 [RFC 7838](https://tools.ietf.org/html/rfc7838)
 
-## What works
-
-- read alt-svc file from disk
-- write alt-svc file from disk
-- parse `Alt-Svc:` response headers, including `ma`, `clear` and `persist`.
-- replaces old entries when new alternatives are received
-- unit tests to verify most of this functionality (test 1654)
-- act on `Alt-Svc:` response headers
-- build conditionally on `configure --enable-alt-svc` only, feature marked as
-  **EXPERIMENTAL**
-- implement `CURLOPT_ALTSVC_CTRL`
-- implement `CURLOPT_ALTSVC`
-- document  `CURLOPT_ALTSVC_CTRL`
-- document `CURLOPT_ALTSVC`
-- document `--alt-svc`
-- add `CURL_VERSION_ALTSVC`
-- make `curl -V` show 'alt-svc' as a feature if built-in
-- support `curl --alt-svc [file]` to enable caching, using that file
-- make `tests/runtests.pl` able to filter tests on the feature `alt-svc`
-- actually use the existing in-memory alt-svc cache for outgoing connections
-- alt-svc cache expiry
-- test 355 and 356 verify curl acting on Alt-Svc, received from header and
-  loaded from cache. The latter needs a debug build since it enables Alt-Svc
-  for plain HTTP.
-
-## What is left
-
-- handle multiple response headers, when one of them says `clear` (should
-  override them all)
-- using `Age:` value for caching age as per spec
-- `CURLALTSVC_IMMEDIATELY` support
-- `CURLALTSVC_ALTUSED` support
-
 # Alt-Svc cache file format
 
 This a text based file with one line per entry and each line consists of nine
@@ -75,6 +27,13 @@ space separated fields.
 4. The ALPN id for the destination host
 5. The host name for the destination host
 6. The host number for the destination host
-7. Within double quotes, the expiration date of this entry
+7. The expiration date and time of this entry withing double quotes. The date format is "YYYYMMDD HH:MM:SS" and the time zone is GMT.
 8. Boolean (1 or 0) if "persist" was set for this entry
 9. Integer priority value (not currently used)
+
+# TODO
+
+- handle multiple response headers, when one of them says `clear` (should
+  override them all)
+- using `Age:` value for caching age as per spec
+- `CURLALTSVC_IMMEDIATELY` support