add extended get to return expiry on get

Pretty regularly, a user asks for the TTL to be returned as part of the get request.  While this is available as part of the SubDocument API and operations, it's not part of the regular get.

Perhaps we should consider an extended opcode get that would return these values.  Raising this for discussion.

The advantage of doing so is this could be aggregated by ns_server as part of "get" operations. 

The alternative would be to use map the highlevel SDK API for get to always using SubDocument operations.