Support for draft-07?

[handrews]

Hello! If this is still an active project, you may be interested to know that there have been new drafts published adding more features to JSON Schema and cleaning up some oddities.

• draft-05 was a bugfix with no new features or meta-schema
• draft-06 is not entirely backwards-compatible with draft-04 (id became $id, and exclusiveMaximum/exclusiveMinimum became numbers instead of boolean modifiers to maximum/minimums; also added contains, propertyNames, const, examples, and a few more formats)
• draft-07 is backwards-compatible with draft-06 (added if/then/else, contentMediaType/contentEncoding, readOnly, writeOnly and numerous formats; some keywords like readOnly were moved over from hyper-schema b/c they had nothing to do with generating hyperlinks)
• draft-08 will likely be published within the next six months