Implemented NPC special ability 40 'NPC_CHASE_DISTANCE'

Param 0: Sets max distance you need to be away from an npc for it to chase you.
Param 1: Sets min distance you need to be from npc for it to chase you.
Usage: Ideally used with ranged attack npcs / casters who you DO NOT WANT
to chase you unless you get too close or too far or out of sight.