feat(xan): Generate random villages

This algorithm is a little rough around the edges right now, but
generally the idea is we find a relatively closed-off region of the map,
and place rooms randomly on it, expanding them until they run into each
other, then we put doors in the walls of the rooms and a single door
opening into the region. Later on, we'll generate friendly (or
unfriendly!) NPCs to put in those rooms.

Change-Id: Ic989b9905f55ad92a01fdf6db11aa57afb4ce383
Reviewed-on: https://cl.tvl.fyi/c/depot/+/726
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/xanthous/src/Xanthous/Generators/CaveAutomata.hs

@@ -70,6 +70,7 @@ parseParams = Params
       <> Opt.help "Number of generations to run the automata for"
       <> Opt.metavar "STEPS"
       )
+  <**> Opt.helper
   where
     parseChance = readWithGuard
       (between 0 1)