Add argument --latencytask optionini optionlast taskini taskfin

It shows the latency between the TaskInitial and TaskFinal. There are
two mode (inclusive and exclusive) to know the tasks are inside the
latency or not.
Merge pull request #2 from visanz2/master

added new argument (--latencytask)
To extract a latency of a subnetwork (defined by starting task and ending task)