Enhance Functionality allow JSON mapping configurations

[AntonTheDev]

When developing multi-platform applications, at times there is a need to share common configuration that can be used to drive logic in their respective platform. Generally the configurations shared are using JSON format, unfortunately the current USMapperKit script implementation is only driven by plists.

Since plists are just as easily represented in json. The enhancement will update the model generation script to parse json or plists.

[AntonTheDev]

I'll update the script within a week or so, and submit a pull request.