css/include:

This is the standard include directory for css script code.
It is included by default in the include paths of css and pdp++ software.
Thus, code here can be included with a simple #include "xxx.css" in your
css script code.  The environmental variables CSSDIR and PDPDIR (depending
on which application you are running) should be set to the base install
directory (typically /usr/local/pdp++) and this directory should be
PDPDIR/css/include.

