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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/jynx.asm

@@ -0,0 +1,10 @@
+; JynxPokedexEntry: ; 0x1b98c5
+	db "HUMANSHAPE@" ; species name
+	dw 407, 900 ; height, weight
+
+	db   "It has several"
+	next "different cry pat-"
+	next "terns, each of"
+	page "which seems to"
+	next "have its own"
+	next "meaning.@"