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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/poliwrath.asm

@@ -0,0 +1,10 @@
+; PoliwrathPokedexEntry: ; 0x183066
+	db "TADPOLE@" ; species name
+	dw 403, 1190 ; height, weight
+
+	db   "It can use its"
+	next "well-developed"
+	next "arms and legs to"
+	page "run on the surface"
+	next "of the water for a"
+	next "split second.@"