- 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
- 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.
- add a whole lot more test cases to the test suites, particularly boundary
- add more argument passing options a la CGI.pm, ie. 'year'=>1974 or 
- docs: explain about the second-part approximation that bugged Ed. Sabol
- add some form of format specifier to date_string for Gregorian
- Conversion between formats that understand time of dat and ones that don't?