Profiler: functions to study time durations

\Profiler::markDeltaStart();
// some code your want to study
\Profiler::markDeltaStop();

'markDeltaStart' calls are stackable, that is, you may call markDeltaStart() while another markDeltaStart() is active (no call to markDeltaStop() yet)
Merge pull request #63 from jay3/master/chiba2

Profiler: functions to study time durations