NSManager的一个简单demo,产生一多个随机数，然后可以撤销和恢复。-NSManager a simple demo, produces more than one random number, and then you can undo and redo.

在ios系统上，画直线，折线 ，贝塞尔曲线，并实现redo undo 保存功能-On ios system, draw a straight line, polyline, Bezier curves, and to achieve redo undo save function