Using i-d-template

This copies in files from https://github.com/martinthomson/i-d-template

I would thoroughly recommend following the steps here: https://github.com/martinthomson/i-d-template#setting-up-the-editors-copy regarding setting up an editors copy on `gh-pages` and the subsequent travis setup.  Then you will be able to link to https://letsencrypt.github.io/acme-spec/ and have a live, always updated version of the proposed protocol.  It's pretty straightforward.

Actually, since this PR removes the output artifacts, I'd recommend doing that setup first.