gen.pl is a simple Perl script that generates a web site, placed
in the out/ directory, from files in src/, inc/ and run/.

Every file in src/ is copied verbatim to out/, except index.html,
which is processed according to the following rules:

 * Lines beginning with .inc trigger the inclusion of a given file
   in inc/.
 * Lines beginning with .eval trigger the evaluation of the following
   Perl code.
 * Lines beginning with .run trigger the execution of a Perl script
   in run/.
 * All other lines are copied verbatim.

The Perl scripts in run/ are written in such a way that they can
be run both as standalone scripts and as part of the genaration
process.

The resulting out/ directory is to be served by a web server, such
as Apache.

The gen.pl script is to be run regularly via a cron job.