Support for differently-named settings files or structures

[skoczen]

I use project/settings/dev.py/project/settings/production.py or something similar in a lot of projects.

This PR provides a way to explicitly set the project root path, instead of only the magic replace('.settings', '') method.

Thanks for a great project!

If this looks good and gets merged, a quick version bump and pypi release would be awesome, so I can pull our projects off my fork and back on to trunk.

Thanks!

[crolfe]

I'd like to see this change get merged in, as modular settings is a very common pattern.