Support attributes like { width = 30%  }

Thanks for your project.

I would like to use the editor to edit markdown for MkDocs. I would like to be able to use markdown attributes for images eg. 
```{ width = 30% }```

It would be great if the editor could support this syntax (which I think is called Python-Markdown or CommonMark + Extensions).

Sorry I couldn't fill your template in Chinese.