Updated calendar and epoch methods (#7)

- Additional easter & start of season methods that don’t have calendar
in signature.
- easter() day parameter now has type assertion.
- isweekend() and isgood() methods without calendar in signature.
Removed 2nd call to isqueensbirt*()
Refactored AUFCalendar() methods (#7)
Load GB calendar code before non AU

They may be need for other calendars (e.g. EU LIBOR calendar)
Refactored EUTA (#7); fixed EULIBOR calendar
Refactored GB calendars (#7)
Refactorised JPFCalendar() code (#7)
Refactored NZ calendar code (#7)
Refactored US calendar code (#7)
Remove unnecessary tests
Add missing easter method
Fixed typos in AU calendar methods
Fixing typos to calendar methods
Updated isgood & adjust signatures

Calendar argument is now subject to an assertion and defaults to
NoFCalendar()