Add complete v4 support and pull latest test suite

However, the tests break in 12 cases for two different reasons:

1. New formats were added to the test suite, which fail (I didn't look at adding support for these yet)

  Solution: Look into adding support for the formats, but some of them are pretty complex, or I don't quite understand

2. The test suite expects the meta-schema to already be imported and deferenceable at the official URI

  Solution: run the tests after importing the two schemas:

		var v = new jsonschema.Validator();
		v.addSchema(require('./draft03.schema.json'));
		v.addSchema(require('./draft04.schema.json'));
		var errs = v.validate(instance.data, test.schema);

No previously passing tests are failing.

Closes #63, #62, #47, #48