base on https://github.com/levinunnink/Smooth-Line-View
I add new function: undo,redo,clear,eraser,change color,save image to file,save image to album
Smooth & fast line drawing from touch inputs for UIViews using Quartz
base on https://github.com/levinunnink/Smooth-Line-View
I add new function: undo,redo,clear,eraser,change color,save image to file,save image to album