We should change the API to make it friendly for standalone instances and not only clusters:

• ered:connect(Host, Port, Opts) for standalone mode, a single connection to a single node.
• ered:connect_cluster(AddressesAndPorts, Opts) for cluster.
• An ered handle can be represented as a small tuple such as{cluster, Pid}. This is similar to how agen_tcp orssl handle is represented.
• Functions likeered:command(EredRef, Command) can work for cluster and standalone and determine by the ered handle (the small tuple) if it's a cluster instance or a single connection.

#41 should be merged first.

Should we autodetect cluster/standalone mode? We could, for example handle an error response form CLUSTER SLOTS. This is not currently the plan though. Users can explicitly connect to a cluster or a standalone node.