Add JSON archiving/unarching
Any plans to add archiving to the JS API to replace direct access to `MSJSONDataArchiver`? The current toJSON doesn't seem to get everything to recreate the object, example [here](https://sketchplugins.com/d/1127-tojson-couldn-t-get-the-complete-info). 

Maybe this doesn't make sense but for my uses I've wrapped the object in a dict to include the version meta with the object. 
```javascript
{
    "meta": {
        "version": 112
        ...
    },
    object: {
        ...
    }
}
```