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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/weedle.asm

@@ -0,0 +1,10 @@
+; WeedlePokedexEntry: ; 0x181bb4
+	db "HAIRY BUG@" ; species name
+	dw 100, 70 ; height, weight
+
+	db   "The barb on top of"
+	next "its head secretes"
+	next "a strong poison."
+	page "It uses this toxic"
+	next "barb to protect"
+	next "itself.@"