refactor towards pep8

Hello! Sorry if this is the World's Most Annoying pull request, but I'm going to be hacking on a version of gaussfitter that supports fitting to masked arrays. To make it a little easier to contribute and get to know the code a little, I made some changes moving the code closer to the [PEP8](http://legacy.python.org/dev/peps/pep-0008/) style.

This branch more or less passes `pep8 --max-line-length=100 gaussfitter/gaussfitter.py` now, with a little bit of artistic license.