Set up tavis-cl process to regenerate HTML files.

[markafoltz]

Right now we have our generated HTML files checked into Git, which isn't great because merging any PR into trunk creates conflicts with all other open branches that Git can't automatically resolve.
(Bikeshed includes some hash of the document in the generated HTML.)

I am wondering if we can set up a tavis-cl workflow to re-generate the HTML on a commit so we can avoid this situation.

[tidoust]

The How to Auto-Deploy Bikeshed Specs guide details steps needed to do that. The main thing being that we'll need two branche (e.g. master with the source code and gh-pages with the generated spec)

[markafoltz]

Thanks @tidoust! As we discussed, it should be okay to make gh-pages the publication branch (as that's the standard across other specs). Folks with open pull requests will need to adjust the base branch through the WebUI or the git commandline.

https://help.github.com/en/articles/changing-the-base-branch-of-a-pull-request

CC @pthatcherg @takumif

[markafoltz]

And let's call the base branch "master".