Rename all files in data/pokedex/entries/

Some people suggested this would be a good idea, and make management of
the files easier. I'm inclined to agree.

data/pokedex/entries/farfetch_d.asm

@@ -0,0 +1,10 @@
+; FarfetchDPokedexEntry: ; 0x1b876c
+	db "WILD DUCK@" ; species name
+	dw 207, 330 ; height, weight
+
+	db   "In order to pre-"
+	next "vent their"
+	next "extinction, more"
+	page "people have made"
+	next "an effort to breed"
+	next "these #MON.@"