Added DetectTouchEvent function to easily add touch event for a GameObject

Added detect touch function to easily add touch event for an object with `Collider2D`.
In this case for example, when you want to create a button, just attach a `Collider2D` and add following functions to `MonoBehavior`:

```
	void TouchBegin (TKTouch evt) {
		//Do something when user first time touch this object
	}
	
	void TouchMoveEnter (TKTouch evt) {
		//Do something when user move his/her finger to this object
	}

	void TouchMoveLeave (TKTouch evt) {
		//Do something when user leave his/her finger to this object but still touching screen
	}

	void TouchEnded (TKTouch evt) {
		//Do something when user stop touching this object
	}
	
	void TouchCanceled (TKTouch evt) {
		//Do something when touching is canceled
	}
```