stopwatch into framework

[ikwattro]

@bachmanm please tell me what you think.

Good replacement for manually using System.currentTimeMillis() :

Example :

Stopwatch stopwatch = new Stopwatch();

stopwatch.start("engine1");
// find candidates()
Event e1 = stopwatch.stop("engine1");
System.out.println(e1.duration());

stopwatch.start("complexWorker");
stopwatch.lap("complexWorker");
stopwatch.lap("complexWorker");
Event e2 = stopwatch.stop("complexWorker");
System.out.println(e2.duration());
System.out.println(e2.getPeriods.get(0).duration());