Calculate Business Days Between Two Dates in a Given QuantLib Calendar
Source:R/bizdays_between.R
      bizdays_between.RdWrapper around qlcal::businessDaysBetween() that allows the use of a
specified calendar without making persistent changes to which calendar is in
use globally.
Arguments
- from, to
- start and end dates. Date object or something coercible with - as.Date().
- calendar
- (character) A QuantLib calendar id (the vector qlcal::calendars lists all valid options). 
- include_first, include_last
- (logical) Whether to include the first and last dates in the count. Defaults to - TRUE.