Added BSD LICENSE file

I noticed the repository had no LICENSE file, and `setup.py` says "BSD License", so I added a BSD license to the repository. I hope that's ok. It's the 3-clause BSD ("new BSD") license, to be more specific.

Also, I noticed your testing is in a function; if its OK with you, I'm going to submit another pull request switching it over to the `unittest` module. It should work pretty much the same way, but using `unittest` has some advantages, especially for forward compatibility and working with `nose`.