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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/diglett.asm

@@ -0,0 +1,10 @@
+; DiglettPokedexEntry: ; 0x182b30
+	db "MOLE@" ; species name
+	dw 8, 20 ; height, weight
+
+	db   "It digs under-"
+	next "ground and chews"
+	next "on tree roots,"
+	page "sticking its head"
+	next "out only when the"
+	next "sun isn't bright.@"