title: Get offset of node within rapidjson?
body: <p>I am deserializing a json string into an object using rapidjson.   When I encounter an issue, not with the structure of the json, but with the content, I want to report an error stating the offset of where the problem is.    </p>
  
  <p>Unfortunately, unless it is a  parse error, I don't see where I can get the current offset of a Value within a Document.   Anyone have any ways of accomplishing this?</p>
  
  <p>For example:</p>
  
  <pre><code>Document doc;
  doc.Parse&lt;0&gt;(json.c_str());
  if( doc.HasMember( "Country" ) ) {
      const Value&amp; country_node = doc["Country"];
      if( !isValid(country_node.GetString()) )
          cout &lt;&lt; "Invalid country specified at position " &lt;&lt; country_node.Offset()?????
  }
  </code></pre>