Document divergences from NCNv1 protocol #108

While the NCNv1 protocol is fully supported insofar as all functionality is present, there do exist minor divergences from the protocol text:

Article GUID hashes are not actually GUID hashes, though they achieve the same function
Article fingerprints are not 64-character hashes, though they achieve the same purpose
Some calls return HTTP error codes which are not outlined by the specification
The implementation of underspecified behaviour (e.g. entity body data and query parameter data being treated "the same") may differ from the reference implementation
Feeds don't have owners, which affects the update portion of the API

All of this should be properly documented in the readme/manual. Information should be available by combing issues and code comments.