[Experience] Add exp mod to npc types to let a server op change the exp modifier (#1252)

* Add exp mod to npc types to let a server op change the exp modifier a npc gives (useful for custom content)

* Updated version.h

zone/exp.cpp

@@ -215,7 +215,15 @@ uint32 Client::GetExperienceForKill(Mob *against)
 
 	if (against && against->IsNPC()) {
 		uint32 level = (uint32)against->GetLevel();
-		return EXP_FORMULA;
+		uint32 ret = EXP_FORMULA;
+
+		auto mod = against->GetKillExpMod();
+		if(mod >= 0) {
+			ret *= mod;
+			ret /= 100;
+		}
+
+		return ret;
 	}
 
 	return 0;