benchmark json deserializer and optimize duplicated code

[onur-ozkan]

json works fine without any problem as it replaced serde and serde_json. It just needs some refactoring on duplicated blocks.

json was made for replacing 3rd party json deserializer dependencies, so I didn't put much effort on performance in order to have extra time on focusing other tasks. Since json crate successfully replaced serde and finished it's first goal, now, optimizing and benchmarking it's performance is the next important goal.