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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/arcanine.asm

@@ -0,0 +1,10 @@
+; ArcaninePokedexEntry: ; 0x182f1c
+	db "LEGENDARY@" ; species name
+	dw 603, 3420 ; height, weight
+
+	db   "An ancient picture"
+	next "scroll shows that"
+	next "people were"
+	page "attracted to its"
+	next "movement as it ran"
+	next "through prairies.@"