added option to pass in function to get video source (for use with s3 tokens)
added option to pass in function to get video source (for use with s3
tokens)

jesperrasmussen/videojs-playLists,atronov/videojs-playLists,belimawr/videojs-playLists,maurobaraldi/videojs-playLists,oriziv/amp-playlist,jgallen23/videojs-playLists,atronov/videojs-playLists,dangdinhtu2014/videojs-playLists,maurobaraldi/videojs-playLists,jesperrasmussen/videojs-playLists,oriziv/amp-playlist,dangdinhtu2014/videojs-playLists