A tool to generate a plist for all OPTIONS combination

Hello fellow porters!

I wrote an utility called Panopticum [1] that uses Poudriere to build a
given port with every possible OPTIONS setting, generate a packing list
after each build and then combine multiple plists into a single one with
necessary OPTIONS_SUB prepended.

It turned out to be far from a simple task due to possible cases like
%%OPT1%%%%NOOPT2%%%%OPT3_OR_OPT4%%, but after cracking my head for a while
it seems to work correctly now.

The utility is already in the Ports tree under ports-mgmt/hs-panopticum
directory. If you're interested, go ahead and try it out. I'll be happy if
anyone finds it to be useful.

[1] https://foss.heptapod.net/bsdutils/panopticum/