ENH: Implementation of holidays and holiday calendars to be used with the
     CustomBusinessDay offset.  Also add an Easter holiday for use in
     calendars.

     HolidayCalendar changes (class factory, get_calendar, __repr__, and merge functions).

     HolidayCalendar start_date/end_date now public.  Python3 changes and add additional
     tests for functionality.  Also, add release note.