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/ponyta.asm

@@ -0,0 +1,10 @@
+; PonytaPokedexEntry: ; 0x1b84f2
+	db "FIRE HORSE@" ; species name
+	dw 303, 660 ; height, weight
+
+	db   "Training by"
+	next "jumping over grass"
+	next "that grows longer"
+	page "every day has made"
+	next "it a world-class"
+	next "jumper.@"