title: Filter in range of two date fields
body: <p>I have something like this:</p>
  
  <pre><code> class Model(models.Model):
        start = models.DateTimeField()
        end = models.DateTimeField()
  </code></pre>
  
  <p>and I want to get all models that follow the following constraints:</p>
  
  <p>given two query parameters qstart, qend</p>
  
  <ul>
  <li>model.end > qstart</li>
  <li>model.start &lt; q.end</li>
  </ul>
  
  <p>which would give all Model objects that lie between in the range of the two dates. I saw you can do </p>
  
  <pre><code> Model.objects.filter(date__range=[qstart, qend])
  </code></pre>
  
  <p>however, that operates on a single field, where as I need to operate on 2 separate fields.</p>