Changed to setuptools to use 2to3.

Hi, I'm packaging [windspharm for OpenSUSE 13.1](https://build.opensuse.org/package/show/home:ocefpaf/python3-windspharm) and, because this OpenSUSE release uses python3 as default, I made two simple changes in your `setup.py`.

Those changes to allow for a py3k package and they should not break anything for python2 (I tested only with python 2.7).

-Filipe

ps: Thanks for windspharm