Waver 介绍
Waver 是类似 Siri 的波纹曲线。
示例：
Waver * waver = [[Waver alloc] initWithFrame:CGRectMake(0,
CGRectGetHeight(self.view.bounds)/2.0 - 50.0, CGRectGetWidth(self.view.bounds), 100.0)];
__weak Waver * weakWaver = waver;
waver.waverLevelCallback = ^() {
[self.recorder updateMeters];
CGFloat normalizedValue = pow (10, [self.recorder averagePowerForChannel:0] / 50);
weakWaver.level = normalizedValue;
};
[self.view addSubview:waver];