Add conversion from Python AST to MyPy AST

[refi64]

This could be really neat and useful. For instance, one could add mypy support to Hy with this.

It would also allow other linting tools to integrate with mypy.

[gvanrossum]

I don't think this will ever happen, so closing. However, note that @ddfisher is working on converting mypy to use (almost) the official Python ast (however, extracted into a separate 3rd party module and augmented to preserve # type: ... comments in the tree). (@ddfisher, is there an issue where this is being tracked?)

[ddfisher]

There is now! See #1353.