FScript functions for handling date and time

The dates which are handled using these functions are always in "yyyyMMdd" format.

• datesys(): return the system date.
• timesys() : return the system time, using "HHmmssSSS" format.
• datecalc(date, offset) : given the start date and the number or days to add, it returns a new date.
• dateday(date) : return the day of the week for the date given as parameter. Monday is returned as 1, and sunday as 7.
• dateweek(date) : return the iso week numberfor the date given as parameter.