Restore size clamping in rendering

https://www.w3.org/Bugs/Public/show_bug.cgi?id=25660

This was removed in commit 3d05e2e05c72b01404cf290bf07c7f0f367827a7.
Text direction (LRT/RTL) now has no effect on position, so the restored
text is somewhat simpler than the original.
Use positionAlign instead of align for maximum size

This currently does the right thing, but will likely need to be revised
after https://www.w3.org/Bugs/Public/show_bug.cgi?id=26020 is fixed.
Remove trailing period after [CSSVALUES] reference
Add a missing </p>
Merge pull request #112 from foolip/missing-p

Add a missing </p>
Merge pull request #111 from foolip/trailing-period

Remove trailing period after [CSSVALUES] reference
Merge pull request #105 from foolip/maximum-size

Restore size clamping in rendering
Merge branch 'master' into position-size-align

Conflicts:
	webvtt.html