Python `__version__` does not match package release version

[djhoese]

https://github.com/ashb/sphinx-argparse/blob/bf1429aa0a4c51ae63d8d6baca0c163a5c6a3a64/sphinxarg/init.py#L1C5-L1C5

This is not in sync with the released version of 0.4.0. Perhaps this should be included as part of the release process? Or maybe dynamic version numbers? I don't have experience with poetry to know how hard that is (only setuptools experience).