Add ConnectionRegistry to handle multiple connections easier
Allows to specify routingKey before publishing msg.

No change to current behavior. If you specify `routingKey` when you call `publish` method, it stills be used.
Merge pull request #21 from tyx/feature/add-connection-registry

Add ConnectionRegistry to handle multiple connections easier
Merge pull request #22 from tyx/feature/persist-routing-key

Allows to specify routingKey before publishing a msg.