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/zubat.asm

@@ -0,0 +1,10 @@
+; ZubatPokedexEntry: ; 0x18275d
+	db "BAT@" ; species name
+	dw 207, 170 ; height, weight
+
+	db   "During the day, it"
+	next "gathers with"
+	next "others and hangs"
+	page "from the ceilings"
+	next "of old buildings"
+	next "and caves.@"