Draw O's

Draw an O in the specified box number with the specified color.
Move X

Move the X through the squares on the board when pressing the button
connected to digital pin 11. Also, move the code to draw the board into
a separate function to simplify the logic of drawing the X in the first
square when the game starts.
No more blinks

Get rid of the annoying blinking where the board lines cross.
Change shapes

Change between X and O when pressing the stop button (digital pin 12).
Choose space

When you press the stop button, the current piece is assigned to the
selected square, the piece changes and moves to the next space.