- stick some sort of forward_day and back_day methods into the base class
- make things more OO.
- make it impossible to instantiate the base class (ie. make it an ADT).
- move the responsibilty for default constructor from subclasses to base
	class
- make Gregorian inherit from Julian rather than the other way around
- Add more calendars (ie. Islamic)
- Get ahold of my original sources
- make the default constructor initialize using today's date.
