WIP: Decoding function parameters from JSON string

[willemolding]

Here is a proposed solution to parsing the parameters to a function passed as a JSON string.

This current implementation only supports primitives and string arguments but extending it to also accept objects and arrays should not be too difficult.

It uses asm-json-parser which is a module I write for event driven JSON parsing in assemblyscript. Using this to define a parser for a custom class is pretty straightforward and most of this boilerplate will be generated by the transform stage.

Inviting feedback and comments before going further

Closes #4