Better automate release process

[Abscissa]

The release process for this is a pain, I need to better automate it. For reference, to do a release, I currently need to (in mostly this order):

• Double-check travis-ci gives it greenlight.
• Pull any changes from GitHub to my local clone (if I've merged anything through GitHub's UI).
• [Technically optional, but a good idea:] Make sure .travis.yml includes the latest compiler versions. If not, update, retest and fix if needed.
• Make sure I can build the docs successfully (See Build docs as part of github actions #181)
• Update the changelog (and commit & push)
• [Annotated] Tag the release (and commit & push)
• Build the docs (they will automatically pick up and display their own version number as reported by git)
• Upload docs to appropriate versioned directory on the server (and double-check it works).
• Update server configuration so "latest docs version" points to the new version (and double-check it works).
• Draft and post a release announcement for the D.announce newsgroup.

That's too much for what should be a simple task. Not all of it can be automated, but a lot of it can and should be automated.