add period

adds a calendar period to a datetime value

(datetime subject, long years, long months, long days) -> datetime

Adds a calendar period to given subject datetime and returns the result.

Supply negative numbers to effectively subtract a period.

Returns nil if any argument is nil.

Parameters

Name	Type	Description
subject	datetime	The datetime to add a calendar period to
years	long	The years to add
months	long	The months to add
days	long	The days to add