Adds support for `requests`.

Requests wasn't working because it uses urllib3, which uses a custom version of HTTPConnection. I introduced support by mocking and patching this class. Also added tweaks to maintain compatibility with some weird things urllib3 does.

Closes issue #7.
Nit: docstring should prescribe the function or method's effect as a command ("Return this"), not as a description ("Returns that") :) http://www.python.org/dev/peps/pep-0257/