Link up messages to the overall game

Add a "say" function for saying messages within an app monad to the
user, and link everything up to display them and track their history

src/Xanthous/Game/Draw.hs

@@ -8,15 +8,25 @@ import Xanthous.Prelude
 import Brick hiding (loc)
 import Brick.Widgets.Border
 import Brick.Widgets.Border.Style
+import Data.List.NonEmpty(NonEmpty((:|)))
 
 import Xanthous.Data (Position(Position), x, y, loc)
 import Xanthous.Data.EntityMap
 import Xanthous.Entities
-import Xanthous.Game (GameState(..), entities, characterPosition)
+import Xanthous.Game
+  ( GameState(..)
+  , entities
+  , characterPosition
+  , MessageHistory(..)
+  , messageHistory
+  )
 import Xanthous.Resource (Name(..))
+import Xanthous.Orphans ()
 
-drawMessages :: GameState -> Widget Name
-drawMessages _ = str "Welcome to Xanthous! It's dangerous out there, why not stay inside?"
+drawMessages :: MessageHistory -> Widget Name
+drawMessages NoMessageHistory = emptyWidget
+drawMessages (MessageHistory _ False) = emptyWidget
+drawMessages (MessageHistory (lastMessage :| _) True) = str $ unpack lastMessage
 
 drawEntities :: (Draw a, Show a) => EntityMap a -> Widget Name
 drawEntities em@(fromNullable . positions -> Just entityPositions)
@@ -41,5 +51,5 @@ drawGame :: GameState -> [Widget Name]
 drawGame game
   = pure
   . withBorderStyle unicode
-  $   drawMessages game
+  $   drawMessages (game ^. messageHistory)
   <=> border (drawMap game)