Autogenerate JSON-Schema-Test-Suite cases from the referencing cases

[Julian]

It should be possible and reasonably straightforward to take any referencing test, or at least any non-erroring test (which here generally takes the form "create some schemas, maybe set a base URI, then resolve a ref or few and assert against the result being some concrete object") and convert it into a JSON-Schema-Test-Suite test case where we need to express the assertion as a valid-or-invalid instance.

This suite is currently a lot richer than the regular one for $ref-specific tests, so doing so will allow sending tests back into the upstream suite without hand-authoring them.