Some maintenance updates:
* The package now uses a `pyproject.toml` file instead of `setup.rb` for packaging, per [PEP 621](https://peps.python.org/pep-0621/).
* `Requirements.txt` has been accordingly deleted.
* Python 3.6 has been removed from the project classifiers and test grid.
* Build and publish scripts on Github have been accordingly updated.
**Full Changelog**: https://github.com/iluvcapra/pycmx/compare/v1.1.5...v1.2.0