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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/krabby.asm

@@ -0,0 +1,10 @@
+; KrabbyPokedexEntry: ; 0x1b8ddd
+	db "RIVER CRAB@" ; species name
+	dw 104, 140 ; height, weight
+
+	db   "If it is unable"
+	next "to find food, it"
+	next "will absorb"
+	page "nutrients by"
+	next "swallowing a"
+	next "mouthful of sand.@"