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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/dratini.asm

@@ -0,0 +1,10 @@
+; DratiniPokedexEntry: ; 0x1cc761
+	db "DRAGON@" ; species name
+	dw 511, 70 ; height, weight
+
+	db   "It sheds many lay-"
+	next "ers of skin as it"
+	next "grows larger. Dur-"
+	page "ing this process,"
+	next "it is protected by"
+	next "a rapid waterfall.@"