ISOBMFF text tracks and captions
Explicitly stated how WebVTT and TTML text tracks are identified
Fixed up <p> comments
Added alternatie VTTCue mapping for ISOBMFF TTML and 3GPP
ISOBMFF TTML as DataCue
Merge pull request #13 from boblund/IsobmffCaptions

ISOBMFF text tracks and captions