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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/sandshrew.asm

@@ -0,0 +1,10 @@
+; SandshrewPokedexEntry: ; 0x182184
+	db "MOUSE@" ; species name
+	dw 200, 260 ; height, weight
+
+	db   "It prefers dry,"
+	next "sandy places"
+	next "because it uses"
+	page "the sand to"
+	next "protect itself"
+	next "when threatened.@"