Internally the replication class uses this order to pick which server
it should connect to: current connection, one of the slaves, master.
If there is at least 1 slave, connect() will not fail even if master
is undefined. If there are no slaves, connect() will pick master. If
there are no connections registered for replication, connect() will
fail immediatly.
* Renamed SingleConnectionInterface to NodeConnectionInterface since
this name is better and makes even more sense in the context of
cluster and replication scenarios.
* Moved specialized aggregate connections (the ones implementing both
predis and redis cluster and master/slave replication) in a newly
created Predis\Connection\Aggregate sub-namespace.
* Removed the "Connection" part from names of aggregate connection
interfaces in the Predis\Connection\Aggregate sub-namespace.
* Changed "Composable" to "Composite" in the name of interfaces and
classes that can use pluggable protocol processors.