Add stubs for the error handling tests.
Set up the first error handling test, currently failing.
Fix the test for the error handling.
Correct issues with the test suite.

Previously, various Expecta calls were not using the correct methods
(beNil instead of beNil()). This will cause some tests to report false
positives.
Add Rick Harrison's error handling method for testing.
Enhance the behaviour of the response serializer.
Cover the not found error.
DRY up the error spec.
Consolidate all of the successful response specs.
Improve error handling when given certain errors.
Test the rate limiting error response.
Update the link JSON used to something with embedded media.
Add a class for embedded media. Not yet hooked up to RKLink.
RKStringFromSubredditCategory is now a public function.
Switch all custom NSStringFrom methods to an RKStringFrom format.
Add support for the embedded media object on links.
Allow for extra fields in the link embedded media.
Improve the documentation of some moderation methods.
Allow outside use of the RKPagination string functions.
Removed extra forward declarations.