add json parser as extra

[cthulhu-irl]

Description

JSON data format is one of the most common data format used for inter-process communication, e.g. RESTful services.

Parsi as a library to ease making parsers should be able to make a simple and common data format like json parser, and it would be a great demonstration of the parsi library's usage and benchmark test.

Goals

• having a real world data format parser for benchmark.

Definition of Done

• the parser should be able to parse json data samples that cover most of standard json.