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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/granbull.asm

@@ -0,0 +1,10 @@
+; GranbullPokedexEntry: ; 0x1d074a
+	db "FAIRY@" ; species name
+	dw 407, 1070 ; height, weight
+
+	db   "It can make most"
+	next "any #MON run"
+	next "away simply by"
+	page "opening its mouth"
+	next "wide to reveal its"
+	next "big fangs.@"