Implement support for new sub-document mutation protocol.
Implement support for new sub-document mutation protocol.

Change-Id: I757a70739b021b01402026cac68f5ffd26265987
Reviewed-on: http://review.couchbase.org/60007
Reviewed-by: Mark Nunberg <dab05a0fe859c5cb93882b2a75a0d613501b07be@couchbase.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/gocb