Updated code to use b-prefixed strings for Python 2/3 compatibility

Previously, if no `include_paths` were specified in Python 3, you would get an error about the code expecting bytes, but getting a str object instead.

Additionally, when running the tests on Python 3, the same thing would happen.

This commit fixes those issues so that it runs properly on 2 and 3. I ran the unit tests, plus some of my own code on both 2.7 and 3.3.