Upgrade ReSpec to v3.2.25

This gets rid of some stray RDFa that failed to validate:
https://github.com/w3c/respec/pull/350
Drop the [WebVTT] prefix when filing new bugs, as it is redundant
Run format.py
Restore the user-agent-defined edge margin, used to handle overscan

Since commit c2821f7a4170795254403d600350f30f4dc01a3e the reference to
"the 'padding-top' space defined in the next section" is broken.

This restores some of the text removed in commit
3d05e2e05c72b01404cf290bf07c7f0f367827a7

Related to but does not resolve
https://www.w3.org/Bugs/Public/show_bug.cgi?id=25637
Merge the vertical growing left/right cases, for consistency
Revert "Ask for feedback to public-texttracks to keep discussion in one place"
Merge pull request #143 from foolip/overscan

Restore the user-agent-defined edge margin, used to handle overscan
Merge pull request #142 from foolip/run-format

Run format.py
Merge pull request #141 from foolip/no-bug-prefix

Drop the [WebVTT] prefix when filing new bugs, as it is redundant
Merge pull request #140 from foolip/respec-v3.2.25

Upgrade ReSpec to v3.2.25
Merge pull request #144 from w3c/revert-138-public-texttracks

Revert "Ask for feedback to public-texttracks to keep discussion in one ...
Merge branch 'master' into minvtt

Conflicts:
	webvtt.html