Fix setup.py

Hi,

I noticed that `pip install django-behave` doesn't actually install the django_behave directory! I managed to track it down to `packages = ['django-behave']` needing to be `packages = ['django_behave']`.

I'm sending in a quick fix to the above. I've also applied some PEP8 formatting to setup.py, since it seemed to mix tabs with spaces and was confusing my editor.

Cheers,
Adam :)