Changes for version 0.10
- now inherits from Set::IntSpan vis C<parent> pragma.
 - added clone() as an alias to duplicate().
 - on error, now C<confess> is used instead of C<croak>.
 - expanded testing, now with Test::More.
 - minor style adjustments in documentation.
 
Modules
extension for Set::IntSpan to handle islands, holes and covers