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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/quagsire.asm

@@ -0,0 +1,10 @@
+; QuagsirePokedexEntry: ; 0x1d00dd
+	db "WATER FISH@" ; species name
+	dw 407, 1650 ; height, weight
+
+	db   "Its body is always"
+	next "slimy. It often"
+	next "bangs its head on"
+	page "the river bottom"
+	next "as it swims but"
+	next "seems not to care.@"