[MSE] Spec updates published

I have posted more changes to the Media Source
Extensions<https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html>
 spec.

Summary of changes:
Bug 20899 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=20899> - Remove
media segments must start with a random access point requirement.
Bug 21065 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=21065> - Update
example code to use updating attribute instead of old appending attribute.
Remove Source Buffer Model section since all the behavior is covered by the
algorithms now.

Diffs:
https://dvcs.w3.org/hg/html-media/rev/668a1c82fb88

Aaron