tick may not be accurate when high CPU usage

[DennisZhangOiler]

Hi, I am using tick to set a timer, but it seems that it could be not accurate when high CPU usage, I just checked the source code, it simply uses a std::thread::sleep, could you improve this to be more accruate?

[DennisZhangOiler]

Would you mind adding a configuration or policy that sleep uses spin_sleep crate?