Ensure version is in sync

[ConorSheehan1]

The version of this project is tracked in three places.

1. as a git tag (needed for the deploy github action)
2. in __init__.py, (needed for the osxdocker version command)
3. in pyproject.toml (needed for flit / poetry)

Get something to keep these in sync.

• bumpversion? https://github.com/peritus/bumpversion? need to use fork for now: https://github.com/c4urself/bump2version
• issue with poetry? peotry version doesn't bump the value in __version__ python-poetry/poetry#144