Configurable decoder

[lacarvalho91]

We should be able to use this with Confluent Wire Format serialized data. To support this we should enable users to configure a decoder, something like:

decoder {
  type = confluent-wire-format
  schema-registry-url = http://localhost:8080
}

decoder {
  type = avro-binary
}

This would allow us to add optional support for JSON as has been requested before