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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/gloom.asm

@@ -0,0 +1,10 @@
+; GloomPokedexEntry: ; 0x1828a6
+	db "WEED@" ; species name
+	dw 207, 190 ; height, weight
+
+	db   "The smell from its"
+	next "drool-like syrup"
+	next "and the pollen on"
+	page "its petals is so"
+	next "bad, it may make"
+	next "opponents faint.@"