Giving the map a getFeatureInfoForPixel method

This method is an entry point for getting feature information.
Renderers can use a hit canvas or defer to a layer (source) to
get matching features for a pixel.

For now this is only implemented for vector layers, and it uses
a bbox query because we cannot refine the result because of
missing geometry intersection functions yet.

examples/vector-layer.js

@@ -42,6 +42,15 @@ var map = new ol.Map({
   })
 });
 
+map.on('mousemove', function(evt) {
+  var features = map.getFeatureInfoForPixel(evt.getPixel(), [vector]);
+  var info = [];
+  for (var i = 0, ii = features.length; i < ii; ++i) {
+    info.push(features[i].get('name'));
+  }
+  document.getElementById('map').title = info.join(', ');
+});
+
 
 var geojson = new ol.parser.GeoJSON();
 var url = 'data/countries.json';