Include type stubs in package

[vivienm]

Type annotations are provided in the source file magic/__init__.pyi, but are not bundled in the package:

$ python setup.py sdist
$ tar -tvf dist/python-magic-0.4.24.tar.gz | grep /magic/
drwx------ vivien/vivien     0 2021-12-30 10:47 python-magic-0.4.24/magic/
-rw------- vivien/vivien 14964 2021-12-30 10:43 python-magic-0.4.24/magic/__init__.py
-rw------- vivien/vivien  8316 2021-12-30 10:43 python-magic-0.4.24/magic/compat.py
-rw------- vivien/vivien  1168 2021-12-30 10:43 python-magic-0.4.24/magic/loader.py
-rw------- vivien/vivien     0 2021-12-30 10:43 python-magic-0.4.24/magic/py.typed

As a result, they are not available for typechecking when using the package in another project.

To ship them, *.pyi files should be included as part of package_data: https://mypy.readthedocs.io/en/latest/installed_packages.html#making-pep-561-compatible-packages.

[ahupp]

Thank you!