Refactor Sudoku field and solver implementation

main.go

@@ -17,7 +17,7 @@ func main() {
 	solver.Add(&strategies.LastDigit{})
 	solver.Add(&strategies.NakedSingle{})
 	solver.Add(&strategies.HiddenSingle{})
-	game, err := sudoku.New(&parser.PuzzleBank{}, solver, openFile())
+	game, err := sudoku.New(&parser.PuzzleBank{}, solver, openFile(), 2)
 	if err != nil {
 		fmt.Println(err.Error())
 		os.Exit(1)