Dates must be in time-line order

[glebvorobev1]

Hello! Probably have found some inconsistency.

1. interface DayCount:
   public abstract int days(LocalDate firstDate, LocalDate secondDate):
   It says "Params:
   firstDate – the first date secondDate – the second date, which may be before the first date"

2. but at DayCount implementation StandardDayCounts days method does not allow arbitrary args order so second date can not be before the first date anymore

@Override public int days(LocalDate firstDate, LocalDate secondDate) { if (secondDate.isBefore(firstDate)) { throw new IllegalArgumentException("Dates must be in time-line order"); } return calculateDays(firstDate, secondDate); }