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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/mankey.asm

@@ -0,0 +1,10 @@
+; MankeyPokedexEntry: ; 0x182dbd
+	db "PIG MONKEY@" ; species name
+	dw 108, 620 ; height, weight
+
+	db   "It lives in groups"
+	next "in the treetops."
+	next "If it loses sight"
+	page "of its group, it"
+	next "becomes infuriated"
+	next "by its loneliness.@"