getFeatures method and featureInfo templates

To avoid surprises for application developers, this change
creates a new getFeatures method. So it is clear now beforehand
whether features or feature info markup is returned. The result
is now also grouped by layer, so application developers always
have a link between a layer and the feature info it returns.

To make getFeatureInfo return markup for vector layers, this
change also adds a featureInfoFunction property to the vector
layer, which gives developers full control over how features are
rendered to feature info markup.

src/ol/map.js

@@ -440,6 +440,19 @@ ol.Map.prototype.getFeatureInfo = function(options) {
 };
 
 
+/**
+ * Get features for a pixel on the map.
+ *
+ * @param {ol.GetFeaturesOptions} options Options.
+ */
+ol.Map.prototype.getFeatures = function(options) {
+  var layers = goog.isDefAndNotNull(options.layers) ?
+      options.layers : this.getLayers().getArray();
+  this.getRenderer().getFeaturesForPixel(
+      options.pixel, layers, options.success, options.error);
+};
+
+
 /**
  * @return {ol.Collection} Interactions.
  */