Add support to generate Java classes for ig-json-parser

[gnewton]

In addition to supporting the creation of Java/JAXB classes, also support the creation of ig-json-parser Java classes.

https://github.com/Instagram/ig-json-parser

[gnewton]

The json of interest here is the json that chidley has converted from XML. The classes generated by chidley for ig-json-parser are for the same json created by the chidley XML->json application.