3 - An internals change to make this class work with Moose 0.34.
8 - Split main functionality out of sugar sub class_has(), into
9 process_class_attribute(). This makes it easier to create attributes
10 on behalf of other classes.
15 - Inherit from Exporter, rather than trying to import its
16 import(). Unfortunately, older Exporters as shipped with Perl 5.6.x
17 only allow subclassing.
22 - First version, released on an unsuspecting world.