Adt Versions Save

Adds support for mypy 0.812—thanks @alexmusa! This mypy version happens to fix #25 and #26 as well.

Don't install adt tests package (thanks @seanjennings1!)

• Fix compatibility with mypy >= 0.730, plus lots of documentation and test updates (thanks @wchresta!)
• Add private _types field on ADTs to access the constructor types (thanks @SebastienLavoie!)

Add source files to PyPI distribution (thanks, @wchresta!)

Add py.typed file so package is seen as typed (thanks, @moshelooks!)