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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/magby.asm

@@ -0,0 +1,10 @@
+; MagbyPokedexEntry: ; 0x1d140e
+	db "LIVE COAL@" ; species name
+	dw 204, 470 ; height, weight
+
+	db   "It naturally spits"
+	next "an 1100-degree"
+	next "flame. It is said"
+	page "when many appear,"
+	next "it heralds a"
+	next "volcanic eruption.@"