title: How to sort fancytree nodes with folders at the top
body: <p>I've reviewed the docs and examples for fancytree for hours soaking up all of fancytree's goodness like a sponge but I can't seem to figure how to sort my fancytree object with folders first by using the API calls. I've initially got around the problem by arranging my initial JSON data so that it's already sorted with folders at the top (a requirement of the project) but now I need to add a new folder to the tree and I need to re-sort the object making sure the newly added folder appears at the top of the tree with the others. </p>
  
  <p>I notice there is a curious option for sortChildren() that allows for a defining a custom compare function but I'm having trouble wrapping my head around how to use it.</p>
  
  <p>Any ideas would be much appreciated!</p>
  
  <p>Snippet below on how I am doing things currently (I am populating the new child with data from some form elements):</p>
  
  <pre><code>//add the new foldername to the tree and re-order
  var rootNode = jQuery("#document_objects").fancytree("getRootNode");
  var childNode = rootNode.addChildren({
      title:    jQuery('#newfoldername').val(),
      tooltip:  jQuery('#description').val(),
      folder:   true
  });
  
  rootNode.sortChildren(null, true);
  </code></pre>
  
  <p>Thanks in advance!</p>