Kn rapidjson

First attempt incorporating rapidjson into colony.

Major parts:
* Parse: parses stringified json into lua tables and deals with parsing errors
* Stringify: stringifies lua tables into strings

Stringify replacer functions/arrays are working as well as stringify spacers.
Review all of this. Recommend changes to the Lua/C as much as your heart desires (optimizations/fixes welcome)
Every instance of `replacer` being invoked should pass `value` as the first argument instead of `nil` (as you have here). This allows another test/suite/json.js test to pass.