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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/pupitar.asm

@@ -0,0 +1,10 @@
+; PupitarPokedexEntry: ; 0x1d1709
+	db "HARD SHELL@" ; species name
+	dw 311, 3350 ; height, weight
+
+	db   "It will not stay"
+	next "still, even while"
+	next "it's a pupa. It"
+	page "already has arms"
+	next "and legs under its"
+	next "solid shell.@"