Oslex

Fix python 3.6-3.8 compatibility issue https://github.com/petamas/oslex/issues/1

Thanks dragonwit for reporting and YUKI2eN3e for fixing the issue!

PyPI release: https://pypi.org/project/oslex/0.1.3/

Add py.typed marker file to allow mypy and similar tools to use `oslex`'s type annotations

Fix minimum required Python version due to https://github.com/smoofra/mslex/issues/1

Also, fix/extend some comments in the code.

First release.