title: DRF: custom ordering on related serializers
body: <p>I've got two serializers one for an Instructor and one for a Course. The Instructor serializer has a defined relationship to the courses like so:</p>
  
  <p><code>courses = CourseSerializer(many=True, read_only=True)</code></p>
  
  <p><strong>How do I specify an order to the courses in the instructor serializer?</strong></p>
  
  <p>Note: I have defined the <code>ordering</code> value in the Course Meta class, but it is the default sorting I want everywhere else. What I want is a custom ordering for api output (specifically dept, number, -semester rather than the default -semester).</p>