Add debug command to reveal the game

Add a (debug) command to reveal all tiles on the game regardless of the
character's vision, which'll make it easier to debug creature's behavior
while they're not visible.

src/Xanthous/App.hs

@@ -155,6 +155,13 @@ handleCommand Open = do
 
 handleCommand Wait = stepGame >> continue
 
+handleCommand ToggleRevealAll = do
+  val <- debugState . allRevealed <%= not
+  say ["debug", "toggleRevealAll"] $ object [ "revealAll" A..= val ]
+  continue
+
+--------------------------------------------------------------------------------
+
 handlePromptEvent
   :: Text -- ^ Prompt message
   -> Prompt AppM