Registers the callbacks specified by the C<reh_config *> object C<cfg> under the given name C<key>.
C<cfg> can be a pointer to a static object of type C<reh_config>.
Registers the callbacks specified by the C<reh_config *> object C<cfg> under the given name C<key>.
C<cfg> can be a pointer to a static object of type C<reh_config>.