Mypy integration for type inference and combined 2+3 codebase

[datnamer]

This looks fantastic.

@JukkaL on the mypy team is looking at a static compile capability using mypy here : python/mypy#1862

Referencing pyir ideas here: https://docs.google.com/document/d/1jGksgI96LdYQODa9Fca7EttFEGQfNODphVmbCX0DD1k/edit

Perhaps these efforts could be combined so that a standard mypy/python typed IR can be emmited that grumpy can consume?

This would have the following advantages:

1. Integration with type hints for large codebases
2. improved type inference for fast code
3. Potentially making 2+3 support easier
4. development synergy with dropbox (and maybe other players below)

I might be dreaming but perhaps Pyjion (@brettcannon et al) and Numba (@seibert, @pzwang et al) can get in on this as well. I think it would be mutually beneficial for python and it's users.

[datnamer]

For py3 the new variable annotation and frame eval api might help here.