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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/charmander.asm

@@ -0,0 +1,10 @@
+; CharmanderPokedexEntry: ; 0x1817db
+	db "LIZARD@" ; species name
+	dw 200, 190 ; height, weight
+
+	db   "If it's healthy,"
+	next "the flame on the"
+	next "tip of its tail"
+	page "will burn vigor-"
+	next "ously, even if it"
+	next "gets a bit wet.@"