title: Fixed icon size in OpenLayers 3
body: <p>I searched for 2 hours now, but it's still not clear if it's possible or not in OL3.
  I would like my icons to be fixed size (not to the screen, but to the image map I'm using). I mean, it should cover the same area even if I'm zoomed out, and not covering the half of the map (like I was using a circle polygon, but I have complex Icons so I have to use it as point features). Is there any solution to it? 
  Like in QGIS: MAP UNITS.</p>
  
  <p>I already have these:</p>
  
  <pre><code>var jelekStyle = function(feature, resolution) {
                  if(feature.get('tipus')=== 'falu') {
                      icon = '00_ikonok/falu.png',
                      size = [115, 233],
                      scale = 0.05,
                      anchor = [0.5,46];
                  }   else if(feature.get('tipus')=== 'puszta') {
                      image = '00_ikonok/puszta.png';
                  }   ...
                  }
  
                    return [new ol.style.Style({
                      image: new ol.style.Icon({
                          src: icon,
                          scale: scale,
                          size: size,
                          anchor: anchor,
                          anchorXUnits: 'fraction',
                          anchorYUnits: 'pixels'
                          })
                    })];
                  };
  </code></pre>
  
  <p>...</p>
  
  <pre><code>var jelek = new ol.layer.Vector({
                      source: new ol.source.Vector({
                      url: 'sopron_honlap/json/Gorog-Kerekes_Sopron_jelek_GeoJSON.geojson',
                      format: new ol.format.GeoJSON()
                      }),
                      updateWhileAnimating: true,
                      updateWhileInteracting: true,
                      style: jelekStyle
                  });
  </code></pre>