json parser proposal

[huangminghuang]

Propose to use abieos for parsing json.

[bhazzard]

Larger initiative needs to:

• Maintain or improve performance
• Simplify codebase (reduce dependencies)

To simplify codebase, remove:

• fc reflect
• fc variant & mutable variant
• fc raw serialization
• abi serializer

Abieos Core should replace all the fc dependencies above, but will not replace the ABI Serialization functions, so we should rethink nomenclature.

The current proposal seeks to address performance, but does not address simplification. This proposal may be the first milestone of the larger initiative.