Script or makefile for manual builds

[hugovk]

Let's create an easy way to run manual rebuilds on the server. This can be for a single version or multiple.

We'll need to do it fairly regularly for the occasional security versions, which are not automatically rebuilt.

We need to make sure all the env vars are set, such as PYTHON_DOCS_ENABLE_ANALYTICS=1 (see #265).

This could be a bash script, or Makefile, or something else.

[AA-Turner]

Currently, salt manages four environment variables: SENTRY_DSN (for Sentry reporting), FASTLY_SERVICE_ID and FASTLY_TOKEN (for purging the CDN), and PYTHON_DOCS_ENABLE_ANALYTICS=1, to add the analytics scripts.

We could add PYTHON_DOCS_ENABLE_ANALYTICS=1 to build_docs.py itself, but the other variables should be kept secret. Currently, we need to manually export them into a shell when doing rebuilds for everything to work as expected.

A

[ewdurbin]

#269 (nice) is an option. if it's acceptable I can update psf-salt and I think we're done here.