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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/sneasel.asm

@@ -0,0 +1,10 @@
+; SneaselPokedexEntry: ; 0x1d097a
+	db "SHARP CLAW@" ; species name
+	dw 211, 620 ; height, weight
+
+	db   "This cunning"
+	next "#MON hides"
+	next "under the cover"
+	page "of darkness,"
+	next "waiting to attack"
+	next "its prey.@"