Add move procs.

'makeMove' advances the game by one turn, switches the current player
and updates the game result.

tests/testMoves.nim

@@ -0,0 +1,85 @@
+import unittest, options
+
+import libmttt
+
+suite "Test the move procedures":
+  setup:
+    var
+      player1 = Player(name: "Adam")
+      player2 = Player(name: "Eve")
+      game: GameState = newGame(player1, player2)
+
+  test "Inital state":
+    check game.currentPlayer == player1
+    check game.players == [player1, player2]
+    check game.turn == 0
+    check game.currentBoard.isNone
+    check game.result == mFree
+
+  test "First move":
+    game = game.makeMove((1, 1), (1, 1))
+    check game.currentPlayer == player2
+    check game.turn == 1
+    check game.currentBoard == (1, 1).some()
+    check game.result == mFree
+
+  test "Second move":
+    game = game.makeMove((1, 1), (1, 1))
+    game = game.makeMove((0, 0))
+    check game.currentPlayer == player1
+    check game.turn == 2
+    check game.currentBoard == (0, 0).some()
+    check game.result == mFree
+
+  test "Move on wrong board":
+    game = game.makeMove((1, 1), (1, 1))
+    expect(IllegalMoveError):
+      game = game.makeMove((0, 0), (2, 2))
+
+  test "Move on a taken cell":
+    game = game.makeMove((1, 1), (1, 1))
+    expect(IllegalMoveError):
+      game = game.makeMove((1, 1))
+
+  test "Move out of bounds":
+    expect(IndexError):
+      game = game.makeMove((3, 0), (0, 0))
+
+  test "Player 1 wins the game":
+    let winner = [
+      [mPlayer1, mFree, mFree],
+      [mPlayer1, mFree, mFree],
+      [mPlayer1, mFree, mFree]
+    ]
+    game.board[0][0] = winner
+    game.board[1][1] = winner
+
+    game.board[2][2] = [
+          [mPlayer1, mFree, mFree],
+          [mFree, mFree, mFree],
+          [mPlayer1, mFree, mFree]
+        ]
+    check checkBoard(game.board) == mFree
+    game = game.makeMove((1, 0), (2, 2))
+    check game.result == mPlayer1
+    check game.currentPlayer == player1
+
+  test "The game ends in a draw":
+    let drawn =  [
+      [mPlayer2, mPlayer2, mPlayer1],
+      [mPlayer1, mPlayer1, mPlayer2],
+      [mPlayer2, mPlayer1, mPlayer2]
+    ]
+    for x in 0 .. 2:
+      for y in 0 .. 2:
+        game.board[x][y] = drawn
+
+    game.board[2][2] = [
+      [mPlayer2, mPlayer2, mPlayer1],
+      [mPlayer1, mPlayer1, mPlayer2],
+      [mPlayer2, mFree, mPlayer2]
+    ]
+    check checkBoard(game.board) == mFree
+    game = game.makeMove((2, 1), (2, 2))
+    check game.result == mDraw
+    check game.currentPlayer == player1