title: CouchDb sort posts by a user in descending timestamp order
body: <p>I have posts that have fields like username (author of the post) and timestamp (uploaded time). I am struggling to create a view, which when queried on, grabs posts by a particular user in descending order of the timestamp.</p>
  
  <pre><code>map: function(doc) {
      if (doc.type == 'post'){
          emit(doc.username, [doc._id, doc.timestamp]);
      };
  },
  </code></pre>
  
  <p>I can query documents authored by a particular user but how do I apply descending = true only on the timestamp field?</p>