More clever looking enemies

I've changed the way the enemies move. They used to walk between certain points with a stupid-looking pattern which was easily detected even by an infant. But from now on, the enemies are not as scripted anymore. They change their beahavior all the time, so when they move they might stop for a while, change direction or even do both.

This makes the enemy movement look more "realistic" and it's now much easier and more fun to perform sneak kills!