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/azumarill.asm

@@ -0,0 +1,10 @@
+; AzumarillPokedexEntry: ; 0x1cd771
+	db "AQUARABBIT@" ; species name
+	dw 207, 630 ; height, weight
+
+	db   "The bubble-like"
+	next "pattern on its"
+	next "stomach helps it"
+	page "camouflage itself"
+	next "when it's in the"
+	next "water.@"