Type Hinting

[AndKaminer]

This goes well with #54, but since technically type hinting isn't part of PEP 8, I pulled it out here. Is type hinting something we want to do? We can check it with something like mypy, which can be automated just like unit testing and flake8. Thoughts?

[MarcCote]

Type hinting is always great. I like the idea of running mypy but I wouldn't make it as a mandatory check for now.