Auto-deploying the html version of the spec

Ever since switching to bikeshed, I've been manually updating index.html
once in a while.  This gets tiring after a while.

However, Domenic has posted a nice gist to auto-deploy to gh-pages using
Travis CI. <https://gist.github.com/domenic/ec8b0fc8ab45f39403dd>

This seems like a nice way, is spelled out in pretty good detail and
doesn't use any personal tokens.

To make things simpler (for me), we might have to put back the master
branch.  Then all of your work and patches would need to go to the master
branch instead of gh-pages.  gh-pages will only be for holding the
generated index.html

If we do this right, index.html will be automatically updated when index.bs
is updated with no interactions from anybody.  Hopefully it will also only
get updated if we don't introduce any new additional errors.

I'll let you know if and when these changes happen.  Hopefully it will be
mostly seamless except for possibly doing pull requests on the master
branch instead of gh-pages.