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/vulpix.asm

@@ -0,0 +1,10 @@
+; VulpixPokedexEntry: ; 0x18259b
+	db "FOX@" ; species name
+	dw 200, 220 ; height, weight
+
+	db   "As its body grows"
+	next "larger, its six"
+	next "warm tails become"
+	page "more beautiful,"
+	next "with a more luxur-"
+	next "ious coat of fur.@"