adding in support for basic http auth

Needed basic http auth for use with a specific API, while using goreq. Added it to the request properties as well as added to the test suite to test basic auth.

[FYI: jefftexture and jefftulsa are the same person, just distinct github accounts]
Is this flag necessary?. We could just check for username and password not being null to set the BasicAuth options, What do you think?