Remove weird properties on the WebVTT cue background box

These were added in commits 3d05e2e05c72b01404cf290bf07c7f0f367827a7 and
be09934775d380753873ab9667c70e1b3af43aa3 but don't make sense since the
WebVTT cue background box is a per-cue inline box.
Lowercase the "apply WebVTT cue settings" definition

For consistency with e.g. "collect WebVTT cue timings and settings"
Refactor how and when "apply WebVTT cue settings" is invoked

This factors out the common "Let nodes be" and most importantly makes
the algorithm actually return the CSS boxes.
Remove hidden comments for cue and region settings

These aren't particularly illuminating, and the indentation would get
mangled by format.py. Fixing format.py does not seem worthwhile.
Normalize the style of "Text track ..." in table heading

It looks like the capitalization was accidentally changed in commit
ee3d595280508aa87d74f9f36e84cfa402fec98b.
Move the ruby anonymous box logic back to its original place

This was moved in commit 3d05e2e05c72b01404cf290bf07c7f0f367827a7
but seems to belong better in its original place since it creates
boxes and does not merely set properties.
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".
Remove the region nullification from the parser

Scripts can already get cues into the state that this tries to avoid,
and it seems harmless due to how the rendering algorithm works.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=25948
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
Merge pull request #80 from foolip/xref

Fix a number of cross-reference issues