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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/koffing.asm

@@ -0,0 +1,10 @@
+; KoffingPokedexEntry: ; 0x1b9276
+	db "POISON GAS@" ; species name
+	dw 200, 20 ; height, weight
+
+	db   "If one gets close"
+	next "enough to it when"
+	next "it expels poison-"
+	page "ous gas, the gas"
+	next "swirling inside it"
+	next "can be seen.@"