For cases where it is useful to capture the elapsed time
of a watch and later examine those split times create a
method on the stop watch that allows for these kinds of
captures and iterations that correspond to the common stop
watch split capability.
Also adds basic docstrings to the stop watch public
methods so that people know what they are and can use them.
Change-Id: Ic52ae5dfcca9a117ccd0dda5cc62a14c09e15ce0
9fe99ba710