mypy in a ppb project won't type the ppb module.

[pathunstrom]

Today I learned:

main.py:2: error: Skipping analyzing "ppb.keycodes": module is installed, but missing library stubs or py.typed marker  [import-untyped]

https://mypy.readthedocs.io/en/stable/installed_packages.html#creating-pep-561-compatible-packages

Looks like we need a py.typed file in the package.