ui:util:pager: document Nathan Weizenbaum as author of Ruby inspiration

ui:util:pager: document Nathan Weizenbaum as author of Ruby inspiration

Nathan's post is released under CC BY-SA 3.0 Unported.  According the
the FSF, the CC BY-SA 2.0 Generic was not compatible with BE's GPLv2+
[1].  I expect my Python implementation is sufficiently different from
Nathan's original notes to be classified as "fair use" and not an
"adaptation".

[1]: http://www.gnu.org/licenses/license-list.html#ccbysa