title: Django custom field with 2 fields
body: <p>I found a markdown editor that I'm adapting to make it work well with Django. I would like to have a field to store the raw markdown and one for the compiled HTML for optimization purposes. I want to create a custom field and widget to hide the complexity and make it reusable everywhere on my website.
  In this custom field, I would like to have two textfields but I didn't find if it was possible.
  My other solutions are :  </p>
  
  <ul>
  <li>to have a model with those two fields and my custom field is actually a foreign key to this model. I like this one because doing some migration for everything is really easy, maybe the implementation will be somewhat tricky.</li>
  <li>to create a abstract model with those two fields. I override the save method to fill the html entry</li>
  </ul>