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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/misdreavus.asm

@@ -0,0 +1,10 @@
+; MisdreavusPokedexEntry: ; 0x1d0301
+	db "SCREECH@" ; species name
+	dw 204, 20 ; height, weight
+
+	db   "It loves to watch"
+	next "people it's scar-"
+	next "ed. It frightens"
+	page "them by screaming"
+	next "loudly or appear-"
+	next "ing suddenly.@"