title: Leaflet clustermarker with custom icon
body: <p>I've managed to cluster my markers. What I want to do now is to display a custom icon with the number of points in the cluster, but I can't figure out how to do that or if it's even possible.</p>
  
  <p>I read the documentation and understood that I need to implement my own iconCreateFunction when creating the marker cluster.</p>
  
  <pre><code>addSomeMarkers: function(data, markerProperties) {
     var markers = L.markerClusterGroup({
        iconCreateFunction: function(cluster) {
           // TODO
        }
     });
     ....
  }
  </code></pre>
  
  <p>I know I can return L.divIcon with a custom css class and <code>cluster.getChildCount()</code>, but I can't specify <code>markerProperties.iconUrl</code> as an image that should be displayed.
  I could also use <code>L.icon</code> with my custom icon from <code>markerProperties.iconUrl</code>, but in that case I don't see how I should get <code>cluster.getChildCount()</code> to display.</p>
  
  <p>So what I need is a combination of both. Is there anything like that? And if not, can someone hint a workaround to achieve this?</p>