Linux timerfd for Tokio.
This crates provides tokio-timer-like API
on top of timerfd. timerfd is a Linux-specific API providing timer notifications as
file descriptor read events.
The advantage of timerfd is that it has more granularity than epoll_wait(),
which only provides 1 millisecond timeouts. timerfd API allows for nanosecond
precision, but precise timing of the wakeup is not guaranteed on a normal
multitasking system.