[9fans] libps added to sources

[Peter A. Cejchan]

Thanks to all who helped me! Libps, a native PostScript generating library,
is on contrib:
     /n/sources/contrib/pac/sys/src/lib/libps.tbz

It is a fork from pslib-0.4.1. It is still a big mess, some warnings about
unused vars, etc, during compiling, but a simple testing program links and
works fine.
Maybe it was not the best choice, however , I was not able to find
 alternatives: if you have an idea, please, share.

++pac