Changes for version 0.03
- added set() method. This idea was given by MATSUNO Tokuhiro <tokuhirom at cpan.org>.
- some global variables were changed an inheritable class data (it was provided from Class::Data::Inheritable a base class of Class::DBI). This idea was given by Tatsuhiko Miyagawa <miyagawa at cpan.org>.
an interface to use some pseudo columns