Update replication.md
Changes the CDTReplicator.state property to be equal to CDTReplicatorStatusStopped
if the replication was stopped via a call to CDTReplicator -stop. Otherwise, if
the replication stops on its own because it completes, the status is set to
CDTReplicatorStatusComplete.

Changes the CDTReplicator code to clarify the object's state,
progress (changesTotal and changesProcessed), and messages sent to delegates
during start, stop and updates to the replicator.

Adds tests in ReplicationAcceptance using a delegate to stop replication
immediately after starting.