title: Convert a Django Model Field Choices into a JSON
body: <p>I need to convert a model choices tuple, like this one from the Django docs:</p>
  
  <pre><code>YEAR_IN_SCHOOL_CHOICES = (
  ('FR', 'Freshman'),
  ('SO', 'Sophomore'),
  ('JR', 'Junior'),
  ('SR', 'Senior'),
  )
  </code></pre>
  
  <p>Into a JSON object like this:</p>
  
  <pre><code>[{"id": 'FR', "year": 'Freshman'}, 
   {"id": 'SO', "year": 'Sophomore'},
   {"id": 'JR', "year": 'Junior'},
   {"id": 'SR', "year": 'Senior'}]
  </code></pre>
  
  <p>It's a pretty straightforward conversion, and very common when using forms, but i couldnt find any automatic function in Django that works out-the-box. I think I'm missing something here.</p>