Added factorial and changed interpolation docs

Author: alvinsight

src/math/Math.js

@@ -856,7 +856,7 @@ Phaser.Math = {
     /**
     * A Bezier Interpolation Method, mostly used by Phaser.Tween.
     * @method Phaser.Math#bezierInterpolation
-    * @param {number} v
+    * @param {Array} v
     * @param {number} k
     * @return {number}
     */
@@ -877,7 +877,7 @@ Phaser.Math = {
     /**
     * A Catmull Rom Interpolation Method, mostly used by Phaser.Tween.
     * @method Phaser.Math#catmullRomInterpolation
-    * @param {number} v
+    * @param {Array} v
     * @param {number} k
     * @return {number}
     */
@@ -936,6 +936,24 @@ Phaser.Math = {
         return this.factorial(n) / this.factorial(i) / this.factorial(n - i);
     },
 
+    /**
+    * @method Phaser.Math#factorial
+    * @param {number} value - the number you want to evaluate
+    * @return {number}
+    */
+    factorial : function( value ){
+        if(value == 0) return 1;
+                        
+        var res = value;
+                        
+        while( --value )
+        {
+                res *= value;
+        }
+        
+        return res;
+    },
+
     /**
     * Description.
     * @method Phaser.Math#catmullRom
@@ -1364,4 +1382,4 @@ Phaser.Math = {
 
     }())
 
-};
+};