Computes the approximate number of months between two points in time.
sare datetime structures or timestamps
DateTime structures or timestamps, then
MonthsBetween(t, s) returns the (in general non-integral) approximate number of months between
s, irrespective of the order of
s, based on the assumption that one month is 30.4375 days.
MonthsBetween(date(1980, 05, 20), date(2000, 05, 20))