number of a peculiar day of the week in months
ts=nb_days_permonth(list_years,rank_day)
* list_years = a real vector of size (2 x 1), collecting the years range to deal with
* rank_day = rank of the day in the week (1 for Monday, 2 for Tuesday, ...)
* ts = a tlist, collecting for each month the number of days of rank rank_day in the month