Adds JsonObject for Ruby<->JSON conversions

Handles:
* Key names to JSON camelCase conventions
* JSON to Ruby keys as snake_case
* Sanitizes keys for JSON

USAGE:

obj         = JsonMessage::JsonObject.new(structure)
json_string = obj.to_s
structure   = JsonMessage::JsonObject.parse(json_string)
obj         = JsonMessage::JsonObject.new(json_string)
structure   = obj.value