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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/tangela.asm

@@ -0,0 +1,10 @@
+; TangelaPokedexEntry: ; 0x1b948c
+	db "VINE@" ; species name
+	dw 303, 770 ; height, weight
+
+	db   "During battle, it"
+	next "constantly moves"
+	next "the vines that"
+	page "cover its body in"
+	next "order to annoy its"
+	next "opponent.@"