title: How do I use my leaflet icon definition in my marker definition?
body: <p>I have a leaflet marker defined like this:</p>
  
  <pre><code>    var W0KCN3 = new L.marker(new L.LatLng(39.2859182,-94.667236),{
       opacity: 0.5,
       contextmenu: true, 
       contextmenuWidth: 140,
       contextmenuItems: [{ text: 'Click here to add mileage circles',
       callback: circleKoords}], 
  icon:  firstaidicon,
  title:`marker_1 ` }).addTo(fg).bindPopup(`1&lt;br&gt;Northland ARES Platte Co. Resource Center&lt;br&gt;Kansas City, MO&lt;br&gt;&lt;br&gt;39.2859182, -94.667236&lt;br&gt;EM29PG`).openPopup(); 
  </code></pre>
  
  <p>And I have an icon defined like this:</p>
  
  <pre><code>    // Define a PoiIcon class
  var PoiIcon = L.Icon.extend({
      options: {
          iconSize: [32, 37]
      }
  });
  
  // Create five icons from the above PoiIcon class
  var firstaidicon = new PoiIcon({iconUrl: 'images/markers/firstaid.png'}),
      eocicon = new PoiIcon({iconUrl: 'images/markers/eoc.png'}),
      policeicon = new PoiIcon({iconUrl: 'images/markers/police.png'}),
      skywarnicon = new PoiIcon({iconUrl: 'images/markers/skywarn.png'}),
      repeatericon = new PoiIcon({iconUrl: 'markers/repeater.png'});
  </code></pre>
  
  <p>I want to use the firstaidicon in the marker definition but I'm struggling to make it work. 
  I've tried:</p>
  
  <pre><code>icon:  firstaidicon,
  </code></pre>
  
  <p>But now I'm getting;</p>
  
  <pre><code>Uncaught TypeError: Cannot read property 'createIcon' of undefined 
  </code></pre>
  
  <p>from all kinds of locations in leaflet.js:5
  What am I doing wrong?</p>