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/rapidash.asm

@@ -0,0 +1,10 @@
+; RapidashPokedexEntry: ; 0x1b855e
+	db "FIRE HORSE@" ; species name
+	dw 507, 2090 ; height, weight
+
+	db   "It just loves to"
+	next "gallop. The faster"
+	next "it goes, the long-"
+	page "er the swaying"
+	next "flames of its mane"
+	next "will become.@"