Created standalone file for Snake

I split Snake from games.c, with some optimizations. I renamed some variables, changed some comments, and changed freeArray() to work more generally (currently only meaningful for its use in Tetris). I also fixed a bug that allowed the player to turn right or left twice in quick succession to reverse direction within the snake, triggering a gameloss.

This version of the code includes a placeholder menu. It also includes test input handling for Windows, which can be enabled in Windows by de-commenting everything below the two "/*Windows:*/" tags and commenting everything below the "/*Linux:*/" tags, as well as de-commenting the body of getLeftInput(). The Snake can then be directed with the WASD keys.