Normalize the style of "Text track ..." in table heading

It looks like the capitalization was accidentally changed in commit
ee3d595280508aa87d74f9f36e84cfa402fec98b.
Remove unused and unlikely to be used ReSpec settings
Remove ReSpec settings which have no effect on the output
Remove strange indentation in ReSpec config
Upgrade ReSpec to v3.2.15

The only change in output is that "Draft Community Group Specification"
is now "Draft Community Group Report".
Merge pull request #87 from foolip/upgrade-respec

Upgrade ReSpec to v3.2.15
Merge pull request #86 from foolip/respec-config

Clean up the ReSpec config block
Merge pull request #84 from foolip/normalize-table-headings

Normalize the style of "Text track ..." in table heading
Link VTTRegion to the interface definition
Link to the <audio> and <video> elements
Drop the "dom-" prefix to interface/attribute/function definitions

ReSpec still prefixes them with "dfn-" and they aren't needed to make
the IDs unique.
Fix the links for the VTTCue and VTTRegion constructors
Fix the links to attributes in tables

This includes a typo fix: direction -> vertical