Audacious

This request originates with Forum thread "m3u8 stream will not play", however, there are 2 separate parts to this request and addressed by this patch:

1) Add ability to both read and optionally save playlists in extended m3u format (includes loading & saving of additional metadata). See https://docs.fileformat.com/audio/m3u/

2) Attempt to add ability to play HLS (HTTP Live Streaming) streams. See https://en.wikipedia.org/wiki/HTTP_Live_Streaming

The proposed patch should handle #1 and recognize & enable support for #2 via ffaudio/ffmpeg, which recognizes this format by content. This patch recognizes these as streams and not playlists, resulting in them being added as a single playlist item (which should then be picked up by ffaudio) rather than as a playlist. However, additional work may be needed in the case of Audacious to prevent occasional pcm buffer underruns since these streams are composed of chunks each lasting only a few seconds and each chunk represented by a separate URL. The reason for this playlist-like "chunking" is to enable dymanic ("adaptive") bitrates over varying quality of internet connections. Since ffmpeg supports HLS, I would expect it to be capable of the necessary one+ chunk lookahead buffering necessary to prevent underruns, but ffmpeg with Audacious defaults doesn't seem to always handle it perfectly. I only discovered this issue when converting this patch to Audacious as I am using it w/o this issue (as of recent times / ffmpeg versions) in "some other code" of mine which does some other buffering and separate reader/writer threading stuff needed for video-capability. This is why I'm not submitting this as a standalone pull request, as it will likely require some additional work on your part elsewhere in Audacious (ie. ffaudio?).

HLS is becoming more popular as a streaming format probably due to it's adaptive bitrates and because it originated with Apple.

Test streams: https://ottverse.com/free-hls-m3u8-test-urls/