implement support for .pls and .m3u -playlists

[holiman]

This makes it so one can do

$ go-chromecast -a 192.168.50.88 load https://somafm.com/indiepop64.pls

Maybe this is already supported? I didn't see it, if so.

[holiman]

Modified now, so that it uses the QueueLoad instead. So the playlist is

• Read from either local filesystem or internet,
• Picked apart, and remade into a []mediaItem,
• The mediaItems are sent using QueueLoad

This means that it the Previous/Next works with it too.

[holiman]

Extended with m3u -support, fixes #122

[vishen]

Amazing, thanks for this @holiman !