module Calendar_sig:Calendar interface. A calendar combines a date and a time: it may be seen as a 6-uple (year, month, day, hour, minute, second).
If you only need operations on dates, you should better use a date
implementation (like module
Date). But if you need to manage more precise
dates, use this module. The exact Julian period is now
[January, 1st 4713
BC at midday GMT; January 22th, 3268 AC at midday GMT].
module type S =