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.
- Set::IntSpan::Island - extension for Set::IntSpan to handle islands, holes and covers