Move calculated holiday dates (or any dates) to the nearest weekday
if they are on weekends.
USAGE:
holiday.nearest.weekday(dates.)
REQUIRED ARGUMENTS:
dates.
dates to move to nearest weekday; must be a
timeDate object.
VALUE:
a vector of dates that is the same as the input
vector wherever its dates lie on weekdays, and which has
Sundays moved to Monday, and Saturdays moved to Friday for
weekend dates.