title: How to count the documents returned by a Mango query
body: <p>I have a mango query:</p>
  
  <pre><code>{
    "selector": {
      "age":{
          "$eq": 22
      }
    }
  }
  </code></pre>
  
  <p>I want to know the number of documents that satisfy this criteria.</p>
  
  <p>I know we can use map reduce functions to achieve this, but is there any way to do this by using mango query like using some key like "count" in the query itself as we do for "sort", and "fields".</p>
  
  <p><strong>I am firing mango query through rest client and I want the number of documents as the response of the query.</strong></p>