Clarify extent of return response from a deep update

[mikepizzo]

#363 clarified, for a deep insert, if a response is returned then it must be expanded to include at least the entities and properties specified in the request.

We make no such statement for deep update, which can include created nested entities.

[mikepizzo]

Proposal: specify, in section 11.4.3.1 of [Protocol] (prior to the sentence that reads "Clients MAY associate an id...") that "The response, if any, SHOULD be expanded to include at least the entities and properties specified in the update request."