Python 3 Support & Bugfix for Argument Parser

I tested a few files locally (with `bugjar script.py`), and everything seems to work with both Python 2.7 and 3.4. (Will also need to patch `tkreadonly`. See pybee/tkreadonly#1.) Not sure whether I missed anything though.

Also fixed the shebang line in `setup.py` and a bug (?) in `main.py` where `ArgumentParser` is passed an unknown kwarg `version`. The program doesn’t work at all without the latter.