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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/nidorino.asm

@@ -0,0 +1,10 @@
+; NidorinoPokedexEntry: ; 0x1823fd
+	db "POISON PIN@" ; species name
+	dw 211, 430 ; height, weight
+
+	db   "It is easily"
+	next "agitated and uses"
+	next "its horn for"
+	page "offense as soon as"
+	next "it notices an"
+	next "attacker.@"