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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/umbreon.asm

@@ -0,0 +1,10 @@
+; UmbreonPokedexEntry: ; 0x1d01af
+	db "MOONLIGHT@" ; species name
+	dw 303, 600 ; height, weight
+
+	db   "On the night of a"
+	next "full moon, or when"
+	next "it gets excited,"
+	page "the ring patterns"
+	next "on its body glow"
+	next "yellow.@"