Add backwards compatible syntax for setting JSON editor defaults.
Add api methods for listening for ready/change events.

```js
// Listen for an event
editor.on('change', function() {});

// Stop listening for an event
editor.off('change', my_function);

// Remove all listeners for an event
editor.off('change');

// Remove all listeners for all events
editor.off();
```

The jQuery wrapper emits DOM events like before, so there is no change there.