Smarter schema and mock assertions

[mouadino]

We need more testing helper so the consumer can make sure that the rpc call made is compliant (parameters are of the correct name and type) to the service input argument schema:

This mean that we need to expose the arguments type also, so the spec can look like this:

@lymph.rpc()
@spec(returns=int, id=uuid.UUID)
def get(self, id):
      pass

This way we can expose argument types and check them from out tests.