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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/golbat.asm

@@ -0,0 +1,10 @@
+; GolbatPokedexEntry: ; 0x1827c4
+	db "BAT@" ; species name
+	dw 503, 1210 ; height, weight
+
+	db   "When it plunges"
+	next "its fangs into its"
+	next "prey, it instantly"
+	page "draws and gulps"
+	next "down more than ten"
+	next "ounces of blood.@"