Switching our default branch to gh-pages

In preparation for automated publishing I am switching our default
branch from master to gh-pages as we discussed at the face to face.

http://www.w3.org/2015/10/26-auto-minutes.html#item03

I will be making a few minor modifications to the specs themselves such
as fixing some markup validation and adding editor's W3C id numbers.

-- 
Ted Guild <ted@w3.org>
W3C Systems Team
http://www.w3.org