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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/croconaw.asm

@@ -0,0 +1,10 @@
+; CroconawPokedexEntry: ; 0x1ccc84
+	db "BIG JAW@" ; species name
+	dw 307, 550 ; height, weight
+
+	db   "The tips of its"
+	next "fangs are slanted"
+	next "backward. Once"
+	page "those fangs clamp"
+	next "down, the prey has"
+	next "no hope of escape.@"