Optimize the average function in math.js

Author: rwrountree

src/math/Math.js

@@ -98,13 +98,14 @@ Phaser.Math = {
     */
     average: function () {
 
-        var sum = 0;
+        var sum = 0,
+            argumentsLength = arguments.length;
 
-        for (var i = 0; i < arguments.length; i++) {
+        for (var i = 0; i < argumentsLength; i++) {
             sum += (+arguments[i]);
         }
 
-        return sum / arguments.length;
+        return sum / argumentsLength;
 
     },
 
@@ -146,7 +147,7 @@ Phaser.Math = {
     /**
     * Snap a value to nearest grid slice, using floor.
     *
-    * Example: if you have an interval gap of 5 and a position of 12... you will snap to 10. 
+    * Example: if you have an interval gap of 5 and a position of 12... you will snap to 10.
     * As will 14 snap to 10... but 16 will snap to 15.
     *
     * @method Phaser.Math#snapToFloor