First pass on the logs

The newly-added logs manage a list of messages. Entities do register a
message to it when hitting each other. Display is created, but not yet
added to the layout actually displayed.

squirrelbattle/entities/player.py

@@ -70,7 +70,7 @@ class Player(FightingEntity):
         for entity in self.map.entities:
             if entity.y == y and entity.x == x:
                 if entity.is_fighting_entity():
-                    self.hit(entity)
+                    self.map.logs.add_message(self.hit(entity))
                     if entity.dead:
                         self.add_xp(randint(3, 7))
                     return True