Fixed "wander" goal.

The NPC will now wander randomly. However, this isn't completely
natural. The change in direction is too erratic. And the goal should be
expanded to stay within a certain area.
Minor optimization.
Added roam goal.

This makes the NPC wander aimlessly within a specified series of
location. This is often more suitable than "wander", as that goal will
make the NPC wander over the whole map, which often isn't what you want.