Publicid <-> URN conversion code in Perl

Here are two Perl programs to convert publicids to URNs
and URNs to publicids.  We should publish these on the
Web page as reference code, once they have been checked.
I have run all the examples in the I-D through them.

-- 
There is / one art             || John Cowan <>
no more / no less              || http://www.reutershealth.com
to do / all things             || http://www.ccil.org/~cowan
with art- / lessness           \\ -- Piet Hein