Fix test to test what it claims to.
Add tests for GdsApi::Response and clean up a bit.
Merge ContentApi::Response into parent class

The transforming of web_urls will be useful outside of content_api.
There's no need for this to be a separate class as this behaviour is only activated when explicitly requested.
Move ListResponse up in the namespace

It's going to be used wider than ContentAPI.
Add unit tests for ListResponse
Add more details to comment about relative_urls
Merge pull request #58 from alphagov/response_refactoring

Response class refactoring