NepaliDate
A fully described calendar date in either the Bikram Sambat or Gregorian system.
Mirrors the shared CustomCalendar. era is 1 for AD (Gregorian) and 2 for BS (Bikram Sambat). Weekday and month indices are 1-based (1 = Sunday, 1 = Baisakh / January). Fields that a producing function does not compute are -1.