*: use latest ffmpeg-sys using bindgen

* Update bindings to newest ffmpeg version for new ffmpeg-sys, which is mostly generated by bindgen
* Bring back removed feature flags
* Fix whitespace formating
* Remove prepended enum names to enum variants
* Remove unneeded allows

src/codec/decoder/subtitle.rs

@@ -14,7 +14,7 @@ impl Subtitle {
 		unsafe {
 			let mut got: c_int = 0;
 
-			match avcodec_decode_subtitle2(self.as_mut_ptr(), out.as_mut_ptr(), &mut got, packet.as_ptr()) {
+			match avcodec_decode_subtitle2(self.as_mut_ptr(), out.as_mut_ptr(), &mut got, packet.as_ptr() as *mut _) {
 				e if e < 0 => Err(Error::from(e)),
 				_          => Ok(got != 0)
 			}