Refactor play-game function to be pure

Added arguments for the board and the player sequence to make the play-game a
pure function (uses only arguments passed to it).  There are still some side
effects however that is only in printing out to the standard out.

Using arguments allows you to start the game with different boards and a
different player sequence.  This can be useful for testing purposes too.

src/tictactoe_cli/core.clj

@@ -202,7 +202,7 @@
   "The game loop.
   We iterate through the player sequence (alternate player turns)
   until there is a winner or the board is full."
-  []
+  [starting-board player-sequence]
   (loop [board starting-board
          player-sequence player-sequence]
     (let [winner (winner? board)]
@@ -217,4 +217,4 @@
          (rest player-sequence))))))
 
 
-(play-game)
+(play-game starting-board player-sequence)