Cleanup: moved relationships into own file.

Moved trading and pricing code to another folder, separate files.
NPC: Added further inventory functionality.
Trading: Added price data structure, which allows for setting prices for items. Also includes some default definitions.

trade/trade.lua

@@ -0,0 +1,22 @@
+-- NPC trading abilities by Zorman2000
+
+npc.trade = {}
+
+npc.trade.CASUAL = "casual"
+npc.trade.TRADER = "trader"
+npc.trade.NONE = "none"
+
+function npc.trade.get_random_trade_status()
+	local chance = math.random(1,10)
+
+	if chance < 3 then
+		-- Non-trader
+    return npc.trade.NONE
+	elseif 3 <= chance and chance <= 7 then
+    -- Casual trader
+    return npc.trade.CASUAL
+	elseif chance > 7 then
+    -- Trader by profession
+    return npc.trade.TRADER
+	end
+end