A Timer contains only a time stamp and no extra information; however, it is useful
because (in Offline) the current time is recorded when measurements are made.
type 'a create_argsThe *_args below are instantiated differently for Timers and Probes. See
Profiler_intf below.
module Group : sig ... endA Group provides a way of grouping multiple probes (or timers). Once grouped, one
can measure stats between members of a group -- i.e. the time it takes to get from
one probe to the other in the group, or the change in a metric between two probes in
a group.