Get Sphinx/RTD set up properly

[jdpage]

We're set up on ReadTheDocs (https://jeff65.readthedocs.io/en/latest/) but we're not actually generating real documentation. We should at least be including the specs for now.

Also, the commit hook still needs to be set up. I have the keys for that, so once Sphinx is ready, this needs to be assigned to me to sort that out.

• Set up Sphinx
• Enable RTD webhook

[jdpage]

Looks like the webhook was enabled automatically. I've also set up Sphinx on the master-ocaml branch (see d2a66d4, f197f2a), and you can see them here: https://jeff65.readthedocs.io/en/master-ocaml/