Multiple Levels feex

Before, you could only load one level into the levels[] array, as they
would overlay eachother. That is no moar!
Fyeah makin' shizz better

Level now changes when you reach the end of your current level! Try it
out! Level 2 + 3 are actually kind of difficult; especially with a
barely working gun...

Also feexed the ammo in the HUD.

Zombie spawner retextured (To a phallus-shaped cactus). I think I may
have accidentally broken the zombie texture in the process...

Also added an ammo refill thingy! (I'll make it actually restock your
ammo soon.)