Make objects, properties, timestamps, references JSON-serialisable
Squashme: Add missing unit tests for to_json() methods
Always run test suites for different APIs in the same order
Make property definitions JSON-serialisable and update unit tests
Make class definitions JSON-serialisable and update unit tests
Make schemas JSON-serialisable and update unit tests
Make commits/refs JSON-serialisable and update unit tests
Make object classes JSON-serialisable and update unit tests
Add support for testing the web service with JSON and YAML