Fix compilation of main method when not on supported platform, works as library cross-platform now

src/main.rs

@@ -1,8 +1,13 @@
-use rusty_keys::main_res;
 
+#[cfg(any(target_os = "windows", target_os = "linux"))]
 fn main() {
-    let ret = main_res();
+    let ret = rusty_keys::main_res();
     if let Err(e) = ret {
         println!("fatal error: {}", e);
     }
 }
+
+#[cfg(not(any(target_os = "windows", target_os = "linux")))]
+fn main() {
+    panic!("sorry no main impl for this platform");
+}