用coreAnimation模仿书摘中心的展开按钮封装的一个控件，轻量级，很好用好用，不支持cocoaPod。
//pzxopen按钮初始化
CGRect frame = CGRectMake(0,0, 45, 45);
PZXOpenButton *pzxButton = [[PZXOpenButton alloc]initWithCenterImage:[UIImage imageNamed:@"加号"] hilightedImage:[UIImage imageNamed:@"加号"] centerFrame:frame];
//可以自己设置控件的中心点
pzxButton.foldCenter = CGPointMake(200, 200);
//添加附属按钮
PZXOpenSubButton *itemButton_1 = [[PZXOpenSubButton alloc]initWithImage:[UIImage imageNamed:@"01"] highlightedImage:[UIImage imageNamed:@"01"] buttonFrame:frame];
PZXOpenSubButton *itemButton_2 =[[PZXOpenSubButton alloc]initWithImage:[UIImage imageNamed:@"03"] highlightedImage:[UIImage imageNamed:@"03"] buttonFrame:frame];
//add附属按钮
[pzxButton addSubItems:@[itemButton_1, itemButton_2]];
[self.view addSubview:pzxButton];
//d点击事件代理
-(void)subButtonPressedWithIndex:(NSUInteger)index