Proposed: New JSON-source build tool

This is a huge update - 2 months of work. I've created a new JSON schema (see the FULL proposal: [Proposal: JSON Source File Schema](https://github.com/browscap/browscap/wiki/Proposal:-JSON-Source-File-Schema)), which this new tool uses. The proposal I've created attempts to simplify contributions via GitHub - people can fork the repo, edit the JSON data files, build their own INI files to test, create a Pull Request back to us. The aim of this is to give anyone the ability to help update the INI files, although having the actual files generated by the few project owners.

**More resources:**
* [JSON Schema docs](https://github.com/browscap/browscap/wiki/Resource%3A-User-Agents-Database)
* [Original proposal](https://github.com/browscap/browscap/wiki/Proposal%3A-JSON-Source-File-Schema)