Update Zombies Types

Hey guys!! Im glad to announce the zombie types update!!!!!!!

Now we have 3 types of zombie, they are:

1. Sleeper Zombie -> This one stays asleep until you cross your senses;
2. Walker Zombie -> Will forever walk in random directions unless you approach;
3. Zombie Pursuers -> Slower but don't give up fresh meat

Some optimizations are made, i used the Coroutines theory to generate new zombies and also used a distance to block the generation to spawn zombies when the player is close.