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* Include type hints.
* Convert C module to use PEP 489 multi-phase extension module initialization.
This makes the module ready for Python sub-interpreters.
* Release now includes a universal2 wheel for Python 3.9 on macOS, to work on
Apple Silicon.
* Stop distributing tests to reduce package size. Tests are not intended to be
run outside of the tox setup in the repository. Repackagers can use GitHub's
tarballs per tag.