title: GeoPoint field type in elasticsearch-dsl-py
body: <p>I'm using <code>elasticsearch-dsl-py 0.0.11</code> for <code>ES 1.7</code> and I want to add a <code>GeoPoint</code> type as listed in <code>fields.py</code> :</p>
  
  <pre><code>__all__ = [
      'construct_field', 'Field', 'Object', 'Nested', 'Date', 'String', 'Float', 'Double',
      'Byte', 'Short', 'Integer', 'Long', 'Boolean', 'Ip', 'Attachment',
      'GeoPoint', 'GeoShape', 'InnerObjectWrapper'
  ]
  </code></pre>
  
  <p>But no class named <code>GeoPoint</code> exists and I cannot create a mapping for a location field like this:</p>
  
  <pre><code>location = GeoPoint()
  </code></pre>
  
  <p>What should I do?</p>