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/monsters.py

@@ -44,7 +44,7 @@ class Monster(FightingEntity):
             next_y, next_x = target.paths[(self.y, self.x)]
             moved = self.check_move(next_y, next_x, True)
             if not moved and self.distance_squared(target) <= 1:
-                self.hit(target)
+                self.map.logs.add_message(self.hit(target))
         else:
             for _ in range(100):
                 if choice([self.move_up, self.move_down,