Migrate CI and automation to GitHub actions

[frozencemetery]

(Supersedes #201)

I took the work @atodorov had done and migrated the parts that require additional repo access as well. A couple things to note:

• The official pypi upload action doesn't work on Windows. I'm told this is on purpose, but their suggested workflow is significantly more complex, so I'm keeping the old approach instead.
• I changed the scripts directory to "ci" instead of ".ci" because it was easier to type and it doesn't need to be hidden. I'd change ".github" too if I could :)
• Windows python versions are allowed to float in the last digit now. I think this is a positive change, though it's not required.
• Travis button goes away because we stop using Travis
• Installing packages on Windows is extremely fraught

[frozencemetery]

I have tested the release workflow and know it works in the way I'd expect. This PR will test the PR workflow :)