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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/mr__mime.asm

@@ -0,0 +1,10 @@
+; MrMimePokedexEntry: ; 0x1b97ea
+	db "BARRIER@" ; species name
+	dw 403, 1200 ; height, weight
+
+	db   "It uses the"
+	next "mysterious"
+	next "power it has in"
+	page "its fingers to"
+	next "solidify air into"
+	next "an invisible wall.@"