Add subdirectories to engine/ similar to pokecrystal

engine/events/evolve_trade.asm

@@ -0,0 +1,44 @@
+EvolveTradeMon:
+; Verify the TradeMon's species name before
+; attempting to initiate a trade evolution.
+
+; The names of the trade evolutions in Blue (JP)
+; are checked. In that version, TradeMons that
+; can evolve are Graveler and Haunter.
+
+; In localization, this check was translated
+; before monster names were finalized.
+; Then, Haunter's name was "Spectre".
+; Since its name no longer starts with
+; "SP", it is prevented from evolving.
+
+; This may have been why Red/Green's trades
+; were used instead, where none can evolve.
+
+; This was fixed in Yellow.
+
+	ld a, [wInGameTradeReceiveMonName]
+
+	; GRAVELER
+	cp "G"
+	jr z, .ok
+
+	; "SPECTRE" (HAUNTER)
+	cp "S"
+	ret nz
+	ld a, [wInGameTradeReceiveMonName + 1]
+	cp "P"
+	ret nz
+
+.ok
+	ld a, [wPartyCount]
+	dec a
+	ld [wWhichPokemon], a
+	ld a, $1
+	ld [wForceEvolution], a
+	ld a, LINK_STATE_TRADING
+	ld [wLinkState], a
+	callab TryEvolvingMon
+	xor a ; LINK_STATE_NONE
+	ld [wLinkState], a
+	jp PlayDefaultMusic