New Spawn System!

Today's patch covers two aspects of the demo: a new spawn system and a fix for the "Repair" the Printer job.

The former system for spawning special zombies was not conducive to more special types being added. It also didn't highlight new zombie types when they show up (special zombies have a minimum level number attached before they will spawn). I have overhauled the entire system so that you will see more special zombies, which does have the side effect of making the game more difficult. Please let me know if you think the game is too hard / too easy / just right. Thanks!

I also have (hopefully) fixed an issue that could arise when smashing the hell out of the printer. I found it was possible to fall into the floor, which is... less than ideal. I think I have it resolved now. If you fall through the floor, let me know! :/