WaitForSecondsRealtime

通过继承Unity5.3新加入的CustomYieldInstruction类，即可自定义协程

定义WaitForSecondsRealtime不受Time.timeScale影响

使用方法与WaitForSecond一样

public class WaitForSecondsRealtime : CustomYieldInstruction
{
    private float waitTime;

    public override bool keepWaiting
    {
        get { return Time.realtimeSinceStartup < waitTime; }
    }

    public WaitForSecondsRealtime(float time)
    {
        waitTime = Time.realtimeSinceStartup + time;
    }
}