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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/slowking.asm

@@ -0,0 +1,10 @@
+; SlowkingPokedexEntry: ; 0x1d0292
+	db "ROYAL@" ; species name
+	dw 607, 1750 ; height, weight
+
+	db   "Every time it ya-"
+	next "wns, SHELLDER"
+	next "injects more poi-"
+	page "son into it. The"
+	next "poison makes it"
+	next "more intelligent.@"