Neutron Refactoring

v2_0 -> v2
No options (redesign)
More features (extension-related)
Some bugfixes
The annotation is needed if the AddressPair object is at some point returned by the api and has to be deserialized.
Even when it is not the case, I tend to prefer being consistent and add the "deserialization hints" whenever we add the "serialization ones". But it is just a matter of completeness and a personal feeling :)