Co-op now expanded to 4 players.

Hey, everyone.

I've had a few people request that I up the co-op from 2 players to 4. You asked, so I delivered.

I had to reprogram a lot of the game logic to work for 4 people, so if you try it out, let me know if you find any bugs.

Also fixed a lot of other bugs and made some improvements to Robotics, Cave, and Bio lab.

Thanks everybody!