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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/bellsprout.asm

@@ -0,0 +1,10 @@
+; BellsproutPokedexEntry: ; 0x1b81a1
+	db "FLOWER@" ; species name
+	dw 204, 90 ; height, weight
+
+	db   "If it notices"
+	next "anything that"
+	next "moves, it"
+	page "immediately flings"
+	next "its vine at the"
+	next "object.@"