1. chronometrist-events->time-list -> chronometrist-events->ts-pairs,
now returns a list of ts pairs. Rewritten using cl-loop.
2. chronometrist-time-list->sum-of-intervals ->
chronometrist-ts-pairs->durations, now returns a list of durations in
integer seconds.
3. A critical bug in chronometrist-iso-timestamp->ts was discovered -
we were passing the output of encode-time (via
parse-iso8601-time-string) to (make-ts :unix ...) - the latter expects
a number, not a list.
4. Both chronometrist-task-time-one-day and
chronometrist-events->ts-pairs were checking if a task was still
ongoing. Removed the redundant checking from the former.
5. Updated docstring of chronometrist-active-time-one-day
6. chronometrist-statistics-count-average-time-spent rewritten using
cl-loop
Also, when trying to write tests, I realized that
chronometrist-events-clean has long been removed. Removed a reference
to it from the manual and a docstring.
