PEP8: whitespace fixes

Per issue #96, I used the `pep8` checker to find some extraneous or missing whitespace:

> python /usr/local/lib/python2.7/dist-packages/pep8.py --select=E211 Bicho/

and found all the stuff to change. I then did

> pep8ify -f whitespace_around_operator Bicho/ -w Bicho/
> pep8ify -f whitespace_before_parameters Bicho/ -w Bicho/

to get whitespace in function calls and whitespace around operators more consistent with PEP 8, and I've visually inspected them to ensure that they're just style fixes with no effect on functionality.

This'll make our code more consistent, easier to read, and easier to refactor in the future.