Support validation of draft-04/hyper-schema
Support validation of draft-04/hyper-schema

(Tests are part of the JSON-Schema-Test-Suite submodule; my PR hasn't been
merged upstream yet, though)

Given that I didn't actually need to change anything important to get the
validator to validate test schemas, I'm not entirely convinced that I've
done the right thing here -- or else the architecture of the validators is a
bit overengineered.

ganeshkumar/json-schema,ruby-json-schema/json-schema,openc/json-schema,openc/json-schema,RST-J/json-schema,iainbeeston/json-schema