Datetime Support Functions

Business Day Functions

`busdaycalendar`	A business day calendar object that efficiently stores information defining valid days for the busday family of functions.
`is_busday`(dates[, weekmask, holidays, ...])	Calculates which of the given dates are valid days, and which are not.
`busday_offset`(dates, offsets[, roll, ...])	First adjusts the date to fall on a valid day according to the `roll` rule, then applies offsets to the given dates counted in valid days.
`busday_count`(begindates, enddates[, ...])	Counts the number of valid days between `begindates` and `enddates`, not including the day of `enddates`.