rename get_occurrences to get_occurrences_range
no need to duplicate the loop
rename search_next_occurrences to get_next_occurrences
rename restart_timer to search_next_occurrences
reorganize search_next_occurrences, make it possible to call get_next_occurrences without influencing the timer
pre-sort values
generalize get_next_occurrences
tasklist: auto-refresh when needed