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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/growlithe.asm

@@ -0,0 +1,10 @@
+; GrowlithePokedexEntry: ; 0x182eaa
+	db "PUPPY@" ; species name
+	dw 204, 420 ; height, weight
+
+	db   "It controls a big"
+	next "territory. If it"
+	next "detects an unknown"
+	page "smell, it roars"
+	next "loudly to force"
+	next "out the intruder.@"