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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/pidgeot.asm

@@ -0,0 +1,10 @@
+; PidgeotPokedexEntry: ; 0x181dd7
+	db "BIRD@" ; species name
+	dw 411, 870 ; height, weight
+
+	db   "Its outstanding"
+	next "vision allows it"
+	next "to spot splashing"
+	page "MAGIKARP, even"
+	next "while flying at"
+	next "3300 feet.@"