Consider making this method hidden; only the Scene's generate_json() needn't be hidden.

Also I don't think `generate_json()` is descriptive. Like, right now, I have no idea why I would want to call it. I think it should be something like `Scene.print()` or `Scene.write_input()` or something. Then stuff like VFrame's can have a `_serialization()` method or something. I would encourage us from moving away from the "verb" name generate_json(), and view the JSON serializatin of a VFrame, etc. as just one of its attributes, but that we need to do some processing to form.