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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/houndour.asm

@@ -0,0 +1,10 @@
+; HoundourPokedexEntry: ; 0x1d0eff
+	db "DARK@" ; species name
+	dw 200, 240 ; height, weight
+
+	db   "Around dawn, its"
+	next "ominous howl"
+	next "echoes through the"
+	page "area to announce"
+	next "that this is its"
+	next "territory.@"