started major rework.  Nothing works right now.
Fixed player rendering
Player now works as intended.  Changed Player.size to Player.radius to be more clear.
-Fixed explosions rendering incorrectly.
-Made bullets work.
-Added Entity.Wall bouncing behavior for Player and Ball
-Planned making Entity.Ball class and making Player/Bullet subclasses of Ball to simplify Player/Bullet changes

Need better way to handle corner collision
-Added MainClass
    4 walls and 2 players currently
- fixed redundant alive check in Entity.Bullet
- changed arena and players
- Fixed mouse controls for player 3
Reworked powerups and items.  Items spawn now, but they don't draw or work correctly.
Orbital now works as intended
All items work as intended.  Items spawn randomly.  All that's left is reimplementation of a menu.
Reformatted code and optimized imports.
removed some unnecessary variables
-Reorganized some code in MainClass and made the frame show the FPS
Made MainClass add the game list to the list of entity lists
Fixed bullets still colliding after death
Optimized imports
Beginning menu work
Added pause screen overlay
Completed menu and player selection