rafka 0.6.0

This is a release refactoring the internal data structures of Rafka as detailed in Rafka Rethinking design doc.

Changed

• [BREAKING] Drop support for multiple Consumers per Client. From now on, only a single Consumer can be associated with a Client instance

• [INTERNAL] The ConsumerManager module as well as the respective functionality for managing Consumers has been completely dropped from the source. Now, the handling of Consumers is split between the Server and the respective Client instances.