Modernise packaging

[hugovk]

Follow on from #33.

• Move config to pyproject.toml and remove redundant setup.*
• List myself as a maintainer
• Switch from setuptools to hatchling + hatch-vcs to automatically get version from tag, no more hardcoding
• Add tox for easy testing of multiple Python versions

tox is a handy tool for testing on different Python versions, and takes care of installing dependencies.

tox tips:

# Install or upgrade
python -m pip install -U tox

# Run tests for Python 3.11
tox -e py311

# Run tests for Python 3.8
tox -e py38

# Run linting
tox -e lint

# Run all
tox

# Run all in parallel
tox -p auto

[marcusvolz]

Thank you @hugovk - very much appreciated.

[hugovk]

You're welcome! I'll make a new release to include #32.

Later on, I can add some fun automation to make releasing even easier :)