Allow user to select level of difficulty

• On the main menu, the user has the option to select EASY or HARD level
• Easy level: user can move snake across game board edges
• Hard level: user will die (game over) if the snake hits any game board edges

Add user interface

• Welcomes the user with a main screen
• Displays "Game Over" with the user's final score upon game end

MVP

Achieves the minimum viable product ("MVP") for our open source project, which is a one-player, terminal-based Snake game that can run on Mac OS X. 🎉