Implement and use KATZE_ARRAY_FOREACH_ITEM

Implement and use KATZE_ARRAY_FOREACH_ITEM

Iterating an array by a GList is considerably faster than
continuously retrieving items, however it is also a lot
more complicated. So the new macro takes care of that and
uses a new semi-private function to avoid copying the list.

Note that the macro can't be nested, which basically isn't
useful in practise anyway.