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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/octillery.asm

@@ -0,0 +1,10 @@
+; OctilleryPokedexEntry: ; 0x1d0d42
+	db "JET@" ; species name
+	dw 211, 630 ; height, weight
+
+	db   "Its instinct is to"
+	next "bury itself in"
+	next "holes. It often"
+	page "steals the nesting"
+	next "holes of others to"
+	next "sleep in them.@"