The patch performs an extensive cleanup of nntplib:
 - Change API methods to return strings instead of bytes. This breaks API compatibility, but given that the parameters need to be passed as strings and many of the returned values would need to be passed to other API methods, I consider the current API to be broken. I've discussed this with Brett at the EuroPython sprint, and he agrees.
 - Add tests.
 - Add pending deprecation warnings for xgtitle() and xpath() methods, which are not useful in modern environments.
 - Use named tuples for returned values where appopriate.
 - Modernize the implementation a little bit.
 - Clean up the docstrings.