Split items/ and trainers/ into their data/ and engine/ components

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/scyther.asm

@@ -0,0 +1,10 @@
+; ScytherPokedexEntry: ; 0x1b9851
+	db "MANTIS@" ; species name
+	dw 411, 1230 ; height, weight
+
+	db   "It's very proud of"
+	next "its speed. It"
+	next "moves so fast that"
+	page "its opponent does"
+	next "not even know what"
+	next "knocked it down.@"