add support for configuring couchbase XDCR (replication) and bump to v3.0

needs testing but submitted for early review
that's a bug.  not supporting `fromCluster` here, we are just following CB's approach which expects that the cluster where the operation is invoked is the "`fromCluster`".

it would be interesting to support `fromCluster` in future.  (that was my original thought, maybe i didn't clean it all up.)