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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/espeon.asm

@@ -0,0 +1,10 @@
+; EspeonPokedexEntry: ; 0x1d0155
+	db "SUN@" ; species name
+	dw 211, 580 ; height, weight
+
+	db   "The tip of its"
+	next "forked tail"
+	next "quivers when it is"
+	page "predicting its"
+	next "opponent's next"
+	next "move.@"