This patch adds a new crate: tokio-timer. This crate provides an
efficient timer implemeentation designed for use in Tokio based
applications.
The timer users a hierarchical hashed timer wheel algorithm with six
levels, each having 64 slots. This allows the timer to have a resolution
of 1ms while maintaining O(1) complexity for insert, removal, and firing
of timeouts.
There already exists a tokio-timer crate. This is a complete rewrite
which solves the outstanding problems with the existing tokio-timer
library.
Closes#146.
