Allow user to pass Request object to AuthorizedSession

[brianbao]

Addresses #275.

I also removed **kwargs into the AuthorizedSession object, as the Session object does not allow **kwargs (psf/requests#1034).

If you'd rather keep kwargs we can initialize the parameters in __init__, something like:

for k, v in kwargs.items():
    setattr(self, k, v)

[brianbao]

Hey @theacodes sorry for the bump, is there anything else I should add to this PR to get it merged?

[theacodes]

Thanks, @brianbao!