title: leaflet.js api icons: why do iconAnchor and popupAnchor have different coordinate locations
body: <p>If I configure leaflet icons in the following way, the popup is anchored at the upper left of the the icon.</p>
  
  <pre><code>iconUrl: 'images/Flaticon_10030-16px.png',
  iconAnchor: [0,0],
  popupAnchor: [0,0]
  </code></pre>
  
  <p>Also, with this setting, I'm not sure that the icon anchor is located at the latlng location.</p>
  
  <p>I'm presuming that the coordinates are accepted as x,y, although nowhere have I found that stated.</p>
  
  <p>I would prefer to KNOW something rather than HOW to accomplish something.</p>
  
  <p>Where within the icon's coordinate system is the icon's anchor point? upper left, center, etc?</p>
  
  <p>Is the icon's anchor point also its 0,0 point?</p>
  
  <p>Where within the icon's coordinate system is the popup's anchor point? </p>
  
  <p>Is the popup's anchor point also its 0,0 point?</p>
  
  <p>What is the coordinate relationship between the icon's anchor point and the popup's anchor point?</p>