Checklist for releasing a new version on PyPI

Adapt the version numbers in pygsl/_version.py and setup.cfg
Build the wheels
```
python setup.py sdist
```

Do a test upload

twine upload --repository testpypi dist/*

Try to install it from a docker image

python3 -m pip install --index-url https://test.pypi.org/simple/ pygsl

Clone the repository and run the tests via pytest
Happy? Push to non-testing repository