Working on mutation deserializers.
Refactored more the Avro deserializers and added a bunch of docs. We
need to abstract away the class that the deserializer outputs to make it
work with generic and specific schemas generating Mutation objects as
well as specific POJOs when needed.
Refactored serializer and producer code as well to start using Avro
(specific) records.
More work on the Kafka generic and specific producers.