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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/igglybuff.asm

@@ -0,0 +1,10 @@
+; IgglybuffPokedexEntry: ; 0x1cd32c
+	db "BALLOON@" ; species name
+	dw 100, 20 ; height, weight
+
+	db   "Instead of walking"
+	next "with its short"
+	next "legs, it moves"
+	page "around by bouncing"
+	next "on its soft,"
+	next "tender body.@"