Add details about sequence

[tplooker]

Currently in both the definition of DataVaultConfiguration and EncryptedDocument the term sequence is defined with the following definition

A unique counter for the data vault in order to ensure that clients are properly synchronized to the data vault. The value is required and MUST be an unsigned 64-bit number.

What is presently un-clear is how this value is incremented and how things like validation occurs.

It is my assumption that sequence represents the value of monotonically incrementing counter that is enforced by the EDV server and is incremented each time a change (a document is created, updated or deleted) occurs on the target EDV, is this assumption correct?

If so I'm happy to file a PR with a clarification in the definition offered under DataVaultConfiguration.

My second question is how the value sequence relates in EncryptedDocument. Is this the value of the counter when the document in question was last updated? If so there is the potential to use this value to do primitive conflict resolution, for example a server being able to reject a document update if the request made features an out of date sequence number.

[tplooker]

Discussed on the April 1st call, updated the language above to reflect the current behaviour of the sequence value to be "represents the value of monotonically incrementing counter that is enforced by the EDV server and is incremented each time a change" occurs on the target EDV, thanks @dlongley for clarifying.