Squashed 'json/' changes from 6c303ca..0b8c484

0b8c484 Fix invalid format

git-subtree-dir: json
git-subtree-split: 0b8c484ffc164e85ac0f3410582814718b45ab6a
Update JSON Schema Test Suite

Merge commit '69b18993aa7e2c630745db80df6392a2f758a52e'
Add jsonschema.validators.extend
Deprecate ValidatorMixin.