Support multiple joysticks

Support multiple joysticks by saving the ID of the touch point when a
canvas is touched. Then when a touch is ended anywhere in the document,
each joystick compares the ended touch ID with the touch ID associated
with its canvas to know whether to honor that touch end event.

joy.js

@@ -175,9 +175,11 @@ var JoyStick = (function(container, parameters, callback)
     /**
      * @desc Events for manage touch
      */
-    function onTouchStart(event) 
+    let touchId = null;
+    function onTouchStart(event)
     {
         pressed = 1;
+        touchId = event.targetTouches[0].identifier;
     }
 
     function onTouchMove(event)
@@ -211,10 +213,12 @@ var JoyStick = (function(container, parameters, callback)
             StickStatus.cardinalDirection = getCardinalDirection();
             callback(StickStatus);
         }
-    } 
+    }
 
-    function onTouchEnd(event) 
+    function onTouchEnd(event)
     {
+        if (event.changedTouches[0].identifier !== touchId) return;
+
         pressed = 0;
         // If required reset position store variable
         if(autoReturnToCenter)