Move lots of data tables into individual data/ files

(This is not expected to be their final location, but it makes them easier to relocate when necessary, and easier for users to edit until the whole project's file structure is finalized.)

constants/npctrade_constants.asm

@@ -0,0 +1,21 @@
+; npctrade struct members (see data/npc_trades.asm)
+TRADE_DIALOG  EQU 0
+TRADE_GIVEMON EQU 1
+TRADE_GETMON  EQU 2
+TRADE_NICK    EQU 3
+TRADE_DVS     EQU 14
+TRADE_ITEM    EQU 16
+TRADE_OT_ID   EQU 17
+TRADE_OT_NAME EQU 19
+TRADE_GENDER  EQU 30
+TRADE_PADDING EQU 31
+
+; NPCTrades indexes (see data/npc_trades.asm)
+	const_def
+	const NPCTRADE_MIKE   ; 0
+	const NPCTRADE_KYLE   ; 1
+	const NPCTRADE_TIM    ; 2
+	const NPCTRADE_EMY    ; 3
+	const NPCTRADE_CHRIS  ; 4
+	const NPCTRADE_KIM    ; 5
+	const NPCTRADE_FOREST ; 6