ENH: Add develop option to install, dev tools

I implemented some potential ideas that I've found useful during development on other packages, see what you think. This PR makes the following minor changes:

1. Changes what `nosetests` will output, defaulting to reporting coverage -- this is what the changes in `setup.cfg` do. This is an aesthetic change, see if you think it's worthwhile.

2. Add Makefile. This is nice because one can do `make test` to run tests, and it will automatically clean all the `.pyc` first for safety.

3. Use `setuptools` namespace for installation. This allows for `python setup.py develop`, which makes it easier for people to do development. Making a symlink isn't difficult, but it's not as nice as that one-liner. This does add a dependency on `setuptools`, though, so might not be worth it.

4. Updates `.gitignore` to ignore a couple annoying / irrelevant files.