Name the interface sections like in the HTML spec
Match the capitalization of the "Data model" section titles
Remove a few unused HTML terms

These are unused since commit 970b3a2d425d26e63fe2cd94b030f8f80289af00:
"Remove the extensions to the TextTrack interface"
Remove "case-sensitive" in description of "NOTE" for consistency

No other strings (like "WEBVTT" and "width") say "case-sensitive".
Don't refer to text track cue concepts as attributes

These concepts are part of the model, not the attributes in the API.
Merge pull request #63 from foolip/attribute-values

Don't refer to text track cue concepts as attributes
Merge pull request #60 from foolip/more-section-titles

Fiddle with more section titles
Merge pull request #61 from foolip/rm-unused-terms

Remove a few unused HTML terms
Merge pull request #62 from foolip/case-sensitive-note

Remove "case-sensitive" in description of "NOTE" for consistency