Improve coverage of Organisation class
Improve coverage of Repo and return decoded JSON

Almost all other methods return decoded JSON, not Response objects, so change
the behaviour of the few on Repo that don't.
Allow specification of args to nose
Cleaner request mocking setup

Don't completely reimplement the requests.Response object. Instead, patch an
appropriate part of the Session instance and explicitly construct a
requests.Response object that then has all the correct behaviour (for .json(),
.iter_lines(), and so on.)
Minor cleaning up
Improve coverage of api module