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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/jigglypuff.asm

@@ -0,0 +1,10 @@
+; JigglypuffPokedexEntry: ; 0x182673
+	db "BALLOON@" ; species name
+	dw 108, 120 ; height, weight
+
+	db   "It rolls its cute"
+	next "eyes as it sings a"
+	next "soothing lullaby."
+	page "Its gentle song"
+	next "puts anyone who"
+	next "hears it to sleep.@"