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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/bayleef.asm

@@ -0,0 +1,10 @@
+; BayleefPokedexEntry: ; 0x1cc9e9
+	db "LEAF@" ; species name
+	dw 311, 350 ; height, weight
+
+	db   "The scent that"
+	next "wafts from the"
+	next "leaves on its neck"
+	page "causes anyone who"
+	next "smells it to"
+	next "become energetic.@"