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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/wartortle.asm

@@ -0,0 +1,10 @@
+; WartortlePokedexEntry: ; 0x181993
+	db "TURTLE@" ; species name
+	dw 303, 500 ; height, weight
+
+	db   "Its long, furry"
+	next "tail is a symbol"
+	next "of longevity,"
+	page "making it quite"
+	next "popular among"
+	next "older people.@"