V3 Response API

This commit adds the new response interface for future versions. It adds
common fields and flags, as well as an extensible versioning format (the
'version' field is still retained on top).

All responses now inherit from a common base class, and all response
callback signatures are idential, cutting out the boilerplate required
for creating wrappers.

Change-Id: Ie1e2d9919b0ae4e0ed6974f67fc3f9d8e8a65c00
Reviewed-on: http://review.couchbase.org/38573
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>