项目中经常需要给View, Cell加线，所以基于View封了个扩展

1.支持添加上下左右四个边的线, 功能虽简单，但是很实用！

2.基于VFL 写的自动布局，跟随View的Frame变化而变化！

效果演示

Demo说明

每次白色View高度+20，线的位置都会自动变化！

两张项目中使用的截图！

功能说明:

- (UIView *)addTopLine;                     //leftSpace = rightSapce = 0
- (UIView *)addTopLine:(CGFloat)leftSpace;  //rightSapce = 0
- (UIView *)addTopLine:(CGFloat)leftSpace rightSpace:(CGFloat)rightSpace;

- (UIView *)addLeftLine;                    //topSpace = bottomSpace = 0
- (UIView *)addLeftLine:(CGFloat)topSpace bottomSpace:(CGFloat)bottomSpace;

- (UIView *)addBottomLine;                    //leftSpace = rightSapce = 0
- (UIView *)addBottomLine:(CGFloat)leftSpace; //rightSapce = 0
- (UIView *)addBottomLine:(CGFloat)leftSpace rightSpace:(CGFloat)rightSpace;

- (UIView *)addRightLine;                   //topSpace = bottomSpace = 0
- (UIView *)addRightLine:(CGFloat)topSpace bottomSpace:(CGFloat)bottomSpace;