The new version of traitlets fixes the rendering of the config help that
was over-indented

Fixes license specifiers according to https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

This allows automatic license inspection tools like pip-licenses to correctly categorize this package.

pyproject.toml explains why matplotlib is not a dependency

Python 3.9 is EOL and tests are failing

Python 3.9 is EOL and tests are failing

Fixes license specifiers according to
https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

This allows automatic license inspection tools like pip-licenses to
correctly categorize this package.

Also attempts to fix the test pipeline.

Closes #55 #58 #63