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/nidoran_f.asm

@@ -0,0 +1,10 @@
+; NidoranFPokedexEntry: ; 0x18224b
+	db "POISON PIN@" ; species name
+	dw 104, 150 ; height, weight
+
+	db   "Small and very"
+	next "docile, it pro-"
+	next "tects itself with"
+	page "its small, poison-"
+	next "ous horn when"
+	next "attacked.@"