title: can I obtain a io.Writer from a http.ResponseWriter?
body: <p>I would like to use <code>json.Encoder</code> to write to a <code>http.ResponseWriter</code>.</p>
  
  <p>I wonder, where do I get <code>http.ResponseWriter</code>'s own <code>io.Writer</code> ?</p>
  
  <p>(<code>io.Writer</code> is required as parameter for <code>json.NewEncoder</code>)</p>
  
  <p>any ideas?</p>