2003-09-25 IKEBE Tomohiro <ikebe@edge.co.jp>
* modified equinox algorithm (based on Ruby's holiday.rb)
2003-09-16 IKEBE Tomohiro <ikebe@edge.co.jp>
* Date::Japanese::Holiday is-a Date::Simple.
* includes Sunday, substitute holiday and special holiday.
* some internal method names are changed.
* added functional interface.
2002-12-05 IKEBE Tomohiro <ikebe@edge.co.jp>
* 0.01 original version
* 0.02 fixed Happy Monday calculation.