Add ol.TileCoord.clone

doc/ol3.md

@@ -123,6 +123,7 @@ MVCObject
   unfreeze()
 
 TileCoord
+  clone() -> TileCoord
   getHash() -> number
 
 Tile

src/ol/tilecoord.js

@@ -24,6 +24,14 @@ ol.TileCoord = function(z, x, y) {
 goog.inherits(ol.TileCoord, goog.math.Coordinate);
 
 
+/**
+ * @return {ol.TileCoord} Clone.
+ */
+ol.TileCoord.prototype.clone = function() {
+  return new ol.TileCoord(this.z, this.x, this.y);
+};
+
+
 /**
  * @return {number} Hash.
  */