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/cloyster.asm

@@ -0,0 +1,10 @@
+; CloysterPokedexEntry: ; 0x1b8ad9
+	db "BIVALVE@" ; species name
+	dw 411, 2920 ; height, weight
+
+	db   "Even a missile"
+	next "can't break the"
+	next "spikes it uses to"
+	page "stab opponents."
+	next "They're even hard-"
+	next "er than its shell.@"