Add wrapping <dl> to the lineAlign steps

This was invalid markup, introduced in
https://github.com/w3c/webvtt/pull/116
Adjust the Abstract and SOTD section.
Merge pull request #135 from foolip/wrap-dl

Add wrapping <dl> to the lineAlign steps
Add a missing # to the [RFC2119] reference
Missed a # in reference.
Merge pull request #137 from foolip/rfc2119-link

Add a missing # to the [RFC2119] reference
Change s/MediaA11y/MAUR/ for the reference.

To make it more conformant with the other references.
Merge pull request #136 from silviapfeiffer/ExtendAbstract

Adjust the Abstract and SOTD section.
Merge commit '6a123f490969eb1ee2d420e665187e8732b94432' into position-size-align
Merge commit 'f90aa945151fc5adad84e30b891b9d6e04aa1c92' into position-size-align

Conflicts:
	webvtt.html
Ask for feedback to public-texttracks to keep discussion in one place
Damned typos...
Merge pull request #138 from foolip/public-texttracks

Ask for feedback to public-texttracks to keep discussion in one place
Merge pull request #139 from silviapfeiffer/typo

Damned typos...
Drop the changes related to user-agent-defined edge margins
Merge branch 'position-size-align' into minvtt
Merge branch 'master' into minvtt

Conflicts:
	webvtt.html