Fixed performance issues caused by deepcopy

chess.py

@@ -130,7 +130,9 @@ class Game:
                            "black" : {"queen" : True,
                                       "king"  : True}
                           }
-        self.history.append(deepcopy(self))
+        self.history.append((deepcopy(self.can_castle),
+                             deepcopy(self.board),
+                             self.turn))
 
     def __repr__(self):
         # Unicode board representation
@@ -173,10 +175,10 @@ class Game:
     def timetravel(self, i):
         if i >= len(self.history) or i < 0:
             return False
-        new = self.history[i]
-        self.board = new.board
-        self.turn = new.turn
-        self.can_castle = new.can_castle
+        c, board, turn = self.history[i]
+        self.board = board
+        self.turn = turn
+        self.can_castle = c
         self.index = i
 
     def prev(self):
@@ -253,7 +255,9 @@ class Game:
         self.can_castle[color]["king"]  = False
         self.moves.append(king_move)
         self.turn = invert(self.turn)
-        self.history.append(deepcopy(self))
+        self.history.append((deepcopy(self.can_castle),
+                             deepcopy(self.board),
+                             self.turn))
         self.index += 1
         return True
 
@@ -297,7 +301,9 @@ class Game:
         self.board = new.board
         self.can_castle = new.can_castle
         self.turn = invert(moved.color)
-        self.history.append(deepcopy(self))
+        self.history.append((deepcopy(self.can_castle),
+                             deepcopy(self.board),
+                             self.turn))
         self.index += 1
         return True