Add JSON as serialization option

[panManfredini]

Currently only Avro serialization/deserialization is supported, this can be a bit annoyng, since it comes with:

• Schema Registry
• Defining Data schemas

For some cases it might be just much simpler to define all via JSON.
Using the JSON-RPC2.0 as RPC protocol. It shpuld be pretty stright forward to implement.