(feat) Enhancement with RepeatedTimer by HashedWheelTimer

[SteNicholas]

Motivation:

RepeatedTimer is implementation by java.util.Timer, there are some defects:

1. Timer support for scheduling is based on absolute time.
2. If an exception is thrown TimerTask unchecked.
3. Timer single-threaded tasks, task execution time may be lost or inaccurate.

We need a better implementation based on io.netty.util.HashedWheelTimer of Netty.

Modification:

Modify RepeatedTimer implementation based on HashedWheelTimer.

Result:

Fixes #234

[fengjiachun]

@SteNicholas 建议适当调小单测 RepeatedTimerTest 的 delta，应该对调度时间精度有更高要求了