TTML2 2e Issues

I have triaged the issue list for 2e, moving forward some issues to a 3e
milestone [1]. If you feel strongly that one of these (now) 3e issues
should be dealt with in 2e, then please post a comment in the issue
requesting it be moved back to 2e.

For the remaining 2e open issues, I have now posted PRs for all marked as
substantive. I believe I can deal with the remainder as editorial changes,
of which 9 are left that have no PR [2].

[1]
https://github.com/w3c/ttml2/issues?utf8=✓&q=is%3Aissue+is%3Aopen+milestone%3A3ED
<https://github.com/w3c/ttml2/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+milestone%3A3ED>
[2]
https://github.com/w3c/ttml2/issues?utf8=✓&q=is%3Aissue+is%3Aopen+milestone%3A2ed-fpwd+-label%3A"pr+open"
<https://github.com/w3c/ttml2/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+milestone%3A2ed-fpwd+-label%3A%22pr+open%22>