Add score system to snake game.

[NathanielCoxson]

The snake game should have a feature where the user gains points for each piece of food they are able to eat.

• [x] The score should be displayed at the top of the screen.
• [x] #14
• [x] #10

[NathanielCoxson]

Score feature was added in 2c5113c9d1cc20e0524f3740a81f53af97768b5e.