[MSE] Spec Updates Published

I have published several updates to the Media Source
Extensions<https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html>
spec
in the last week and a half.

Summary of changes:
Bug 21954 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=21954> - Add
[EnforceRange] to appendStream's maxSize parameter.
Bug 21953 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=21953> - Add NaN
handling to appendWindowEnd setter algorithm.
Bug 20901 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=20901> - Remove
AbortMode and add AppendMode.
Bug 21911 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=21911> - Change
MediaPlaybackQuality.creationTime to DOMHighResTimeStamp.

Editorial fixes suggested by Glenn Adams as he has been reviewing the spec:
- Alphabetize definitions section.
- Changed endOfStream('decode') references to make it clear that JavaScript
can't intercept these calls.
- Fix links for all types in the IDL that are defined in external
specifications.
- Reworked ambiguous text in a variety of places.
- Added Acknowledgements section. (If I accidentally left someone out or
misspelled a name, please let me know.)

Diffs:
May 02 : https://dvcs.w3.org/hg/html-media/rev/b60bf8077d9c
May 06 : https://dvcs.w3.org/hg/html-media/rev/9ff5e42736b6
May 13 : https://dvcs.w3.org/hg/html-media/rev/71968956733e

Aaron