Automate publication to pypi

[hillairet]

Use Github actions to publish new releases.

• If we create the tag 0.2.3 and automatically publish to pypi, do we overwrite 0.3?
  • No, pypi parses the version number and will keep 0.3 as the latest

[hillairet]

That's how it can be done.
Notice the on requirement at the top. That looks goooooood!