modified "change" option to get changed json data

Because the data has beed `stringify`ed and `parse`ed when init to strip down non-JSON data types. So the original json data won't changed whenever you access.

The new usage just like:
```javascript
$('#editor').jsonEditor(json, { change: function (jsonChanged) {...} });
```

Another thing should be noticed is that I tried very hard but didn't find your way to minify the code. so the `jquery.jsoneditor.min.js` hasn't been updated.

Hope to be useful.
Thanks.