Use Timer interface instead of HashWheelTimer
Implement a precise, realtime hash wheel timer

This commit implements a realtime, core-occupying hash wheel timer.

It is not to be used in single-core environments, since it will take control
of a core and busy-spin until it's cancelled.

Instead of thread.sleep(), a busy-spin is used here.
Replace TreeSet with ConcurrentSkipListSet, fix order equality problem

All sorted set implementations rely on the fact that equals() is consistent with
compareTo(): http://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html

This was leading to the problem that several parallel registration with same
amount of rounds left were removing each other.

Another problem laid in the fact that TreeSet should either be synchronised or
it can't guarantee consistency of iterator, therefore will throw concurrent
modification exception.

This commit solves both problems.
Merge pull request #275 from ifesdjeen/enchancement-realtime-hash-wheel-timer

Enchancement realtime hash wheel timer