[Quest API] Add Merchant Events to Perl/Lua. (#2452)

- Add EVENT_ALT_CURRENCY_MERCHANT_BUY to Perl/Lua.
- Add EVENT_ALT_CURRENCY_MERCHANT_SELL to Perl/Lua.
- Add EVENT_MERCHANT_BUY to Perl/Lua.
- Add EVENT_MERCHANT_SELL to Perl/Lua.

This will allow server operators to track or do specific stuff based on if a person buys X item from Y NPC or whatever.

zone/event_codes.h

@@ -98,6 +98,10 @@ typedef enum {
 	EVENT_UNEQUIP_ITEM_CLIENT,
 	EVENT_SKILL_UP,
 	EVENT_LANGUAGE_SKILL_UP,
+	EVENT_ALT_CURRENCY_MERCHANT_BUY,
+	EVENT_ALT_CURRENCY_MERCHANT_SELL,
+	EVENT_MERCHANT_BUY,
+	EVENT_MERCHANT_SELL,
 	_LargestEventID
 } QuestEventID;