HLS doesn't adapt

Great lib and am really liking using this as solves a lot of Vitamio issues I was having with playback quality.

One thing I have noticed though is that there is an option in Vitamio for:
mediaPlayer.setAdaptiveStream(true);
which is not available here

Which somehow that I haven't worked out yet makes the ffmpeg hls.c actually switch bitrates on playback.

The standard apple URL for testing this is here: http://devimages.apple.com/iphone/samples/bipbop/bipbopall.m3u8

You will note that it just sits on Gear 1 when it should shift up bitrates. In ffplay command line you can shift up and down by pressing 'v'

Start with the ffmpeg hls.c behavior and the mediaPlayer.setAdaptiveStream(true) reference in the issue, then reproduce with Apple's bipbopall.m3u8 stream. Compare playback with ffplay's bitrate switching and trace the player entry point that handles HLS playback. Done means the stream changes bitrate during playback on the supported platforms.

Written by the indexing model from the issue text.