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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/shuckle.asm

@@ -0,0 +1,10 @@
+; ShucklePokedexEntry: ; 0x1d088e
+	db "MOLD@" ; species name
+	dw 200, 450 ; height, weight
+
+	db   "The fluid secreted"
+	next "by its toes carves"
+	next "holes in rocks for"
+	page "nesting and can be"
+	next "mixed with BERRIES"
+	next "to make a drink.@"