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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/donphan.asm

@@ -0,0 +1,10 @@
+; DonphanPokedexEntry: ; 0x1d10ac
+	db "ARMOR@" ; species name
+	dw 307, 2650 ; height, weight
+
+	db   "Because this"
+	next "#MON's skin is"
+	next "so tough, a normal"
+	page "attack won't even"
+	next "leave a scratch on"
+	next "it.@"