Move trade data, some trade.c clean up documentation

data/event_scripts.s

@@ -27,6 +27,7 @@
 #include "constants/secret_bases.h"
 #include "constants/songs.h"
 #include "constants/species.h"
+#include "constants/trade.h"
 #include "constants/trainer_hill.h"
 #include "constants/trainers.h"
 #include "constants/vars.h"

data/maps/BattleFrontier_Lounge6/scripts.inc

@@ -5,7 +5,7 @@ BattleFrontier_Lounge6_EventScript_264FED:: @ 8264FED
 	lock
 	faceplayer
 	goto_if_set FLAG_BATTLE_FRONTIER_TRADE_DONE, BattleFrontier_Lounge6_EventScript_265083
-	setvar VAR_0x8008, 3
+	setvar VAR_0x8008, INGAME_TRADE_MEOWTH
 	copyvar VAR_0x8004, VAR_0x8008
 	specialvar VAR_RESULT, GetInGameTradeSpeciesInfo
 	copyvar VAR_0x8009, VAR_RESULT

data/maps/FortreeCity_House1/scripts.inc

@@ -5,7 +5,7 @@ FortreeCity_House1_EventScript_2162BB:: @ 82162BB
 	lock
 	faceplayer
 	goto_if_set FLAG_FORTREE_NPC_TRADE_COMPLETED, FortreeCity_House1_EventScript_216355
-	setvar VAR_0x8008, 1
+	setvar VAR_0x8008, INGAME_TRADE_PLUSLE
 	copyvar VAR_0x8004, VAR_0x8008
 	specialvar VAR_RESULT, GetInGameTradeSpeciesInfo
 	copyvar VAR_0x8009, VAR_RESULT

data/maps/PacifidlogTown_House3/scripts.inc

@@ -5,7 +5,7 @@ PacifidlogTown_House3_EventScript_203C11:: @ 8203C11
 	lock
 	faceplayer
 	goto_if_set FLAG_PACIFIDLOG_NPC_TRADE_COMPLETED, PacifidlogTown_House3_EventScript_203CAB
-	setvar VAR_0x8008, 2
+	setvar VAR_0x8008, INGAME_TRADE_HORSEA
 	copyvar VAR_0x8004, VAR_0x8008
 	specialvar VAR_RESULT, GetInGameTradeSpeciesInfo
 	copyvar VAR_0x8009, VAR_RESULT

data/maps/RustboroCity_House1/scripts.inc

@@ -5,7 +5,7 @@ RustboroCity_House1_EventScript_21593F:: @ 821593F
 	lock
 	faceplayer
 	goto_if_set FLAG_RUSTBORO_NPC_TRADE_COMPLETED, RustboroCity_House1_EventScript_2159D5
-	setvar VAR_0x8008, 0
+	setvar VAR_0x8008, INGAME_TRADE_SEEDOT
 	copyvar VAR_0x8004, VAR_0x8008
 	specialvar VAR_RESULT, GetInGameTradeSpeciesInfo
 	copyvar VAR_0x8009, VAR_RESULT