Changelog: Single-player features

Hi!

Quick updates to the game:

- Controls 

    - Can now be found in the main menu. This is toggleable by clicking on the Controls box. Also adds functionality for local multiplayer.

- High Score:

    - The game now does not end when the enemy dies, but a new one is spawned instead. Get the highest win streak possible!

Bug fixes:

- Tanks no longer spawn every time the space button is clicked.

Known bugs:

- In some cases, enemy tanks do not despawn after the game ends if the player loses and restarts.