UIView Touch，觸控事件處理

UIResponser有四個對觸控碰處理的method(interface)介面

UIView與UIViewController 都繼承至UIResponser

因此只要是UIView與UIViewController的子類，實作以下四個method就能對觸控做處理

touchesBegan:withEvent:,
touchesMoved:withEvent:,
touchesEnded:withEvent:,
touchesCancelled:withEvent: