Try using astor for AST printing

[taion]

https://pypi.python.org/pypi/astor

Wanted to let people know I'm working on this. Don't have anything ready to PR yet.

The ideal is that if this integration is possible, then it saves having to write a finicky AST printer for Python, when there already is one.

Ultimately it'd be nice to use standard Python package management instead of vendoring dependencies (for now – since the Python code here has to run in-virtualenv), but that's a longer-term concern that's really more a function of #2.

[taion]

BTW, as a dev thing, astor.rtrip is good for verifying transform correctness.