Add support for ArcGIS Rest Services

Adding a data source to support ArcGIS Map Server and Image Server.
Functionality is similar to the ArcGIS93Rest Layer in OpenLayers 2.

examples/arcgis-tiled.js

@@ -0,0 +1,28 @@
+goog.require('ol.Map');
+goog.require('ol.View');
+goog.require('ol.layer.Tile');
+goog.require('ol.source.MapQuest');
+goog.require('ol.source.TileArcGISRest');
+
+var url = 'http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/' +
+    'Specialty/ESRI_StateCityHighway_USA/MapServer';
+
+var layers = [
+  new ol.layer.Tile({
+    source: new ol.source.MapQuest({layer: 'sat'})
+  }),
+  new ol.layer.Tile({
+    extent: [-13884991, 2870341, -7455066, 6338219],
+    source: new ol.source.TileArcGISRest({
+      url: url
+    })
+  })
+];
+var map = new ol.Map({
+  layers: layers,
+  target: 'map',
+  view: new ol.View({
+    center: [-10997148, 4569099],
+    zoom: 4
+  })
+});