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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/sentret.asm

@@ -0,0 +1,10 @@
+; SentretPokedexEntry: ; 0x1ccd6b
+	db "SCOUT@" ; species name
+	dw 207, 130 ; height, weight
+
+	db   "When acting as a"
+	next "lookout, it warns"
+	next "others of danger"
+	page "by screeching and"
+	next "hitting the ground"
+	next "with its tail.@"