可调节画笔粗细和颜色，可撤销上一步操作或全部操作，具有橡皮擦功能，可以保存图画到本地相册。 -Demo a simple drawing tools, adjustable brush thickness and color can be revoked on the step of the operation or all of the operations with the eraser function, you can save the picture to the local albu

自定义橡皮擦手势，代码可以实现系统自带的单击手势，以及自定义的橡皮擦擦除手势-Custom eraser gestures, the code can achieve the system comes with the click gesture, as well as custom eraser erase gesture