Video/Sound player based on AVPlayer, with OpenGL texture support.
Wrapper around AVPlayer, with CoreVideo support for retrieving the
current frame as an OpenGL rectangle texture.  Some additional
support for playlists and looping, although this might need more work
in the future to try to achieve frame perfect back-to-back playback
and looping, etc.  This should probably deprecate NSSound.

Large contributions by Nick Nikolov.