Sudoku 21

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• Load and save system.
• Undo and redo system.
• Number placing by pressing an empty square.
• Note placing by pressing and holding an empty square.
• Settings for that little tweaking.
• Quick fill that can be activated by pressing a number in the number selector a second time. Once activated pressing a square will go through that square's allowed numbers in an ascending order, and holding will place all allowed notes.