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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/hoppip.asm

@@ -0,0 +1,10 @@
+; HoppipPokedexEntry: ; 0x1cd8b5
+	db "COTTONWEED@" ; species name
+	dw 104, 10 ; height, weight
+
+	db   "It can be carried"
+	next "away on even the"
+	next "gentlest breeze."
+	page "It may even float"
+	next "all the way to the"
+	next "next town.@"