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/blastoise.asm

@@ -0,0 +1,10 @@
+; BlastoisePokedexEntry: ; 0x1819f9
+	db "SHELLFISH@" ; species name
+	dw 503, 1890 ; height, weight
+
+	db   "It firmly plants"
+	next "its feet on the"
+	next "ground before"
+	page "shooting water"
+	next "from the jets on"
+	next "its back.@"