[Python-compilers] Python2/3 ast compatibility

[serge guelton]

Hi all,

As pythran struggled to have a python2/3 ast abstraction, I packed this
minimal package:

    https://github.com/serge-sans-paille/gast

That provides an AST that can represent 2.7, 3.0, 3.1, 3.2, 3.3, 3.4 and
3.5 AST with a limited set of change.

It can be useful for those of us that use the Python AST as input.

Feedbacks appreciated ;-)