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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/weepinbell.asm

@@ -0,0 +1,10 @@
+; WeepinbellPokedexEntry: ; 0x1b81fd
+	db "FLYCATCHER@" ; species name
+	dw 303, 140 ; height, weight
+
+	db   "When it's hungry,"
+	next "it swings its"
+	next "razor-sharp"
+	page "leaves, slicing up"
+	next "any unlucky object"
+	next "nearby for food.@"