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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/stantler.asm

@@ -0,0 +1,10 @@
+; StantlerPokedexEntry: ; 0x1d1174
+	db "BIG HORN@" ; species name
+	dw 407, 1570 ; height, weight
+
+	db   "The round balls"
+	next "found on the"
+	next "fallen antlers can"
+	page "be ground into a"
+	next "powder that aids"
+	next "in sleeping.@"