implement release please so this project starts getting properly versioned.

this project is so popular that it really needs to start properly following semver.

googles release-please github action is the easiest way to implement this.

list of things at minimum that should be done:

- add the release workflow
- if there's a spot in the python code where you've decided to hardcode the version, use release-please annoations on that line to auto bump it when a release is made.