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/rattata.asm

@@ -0,0 +1,10 @@
+; RattataPokedexEntry: ; 0x181e3d
+	db "RAT@" ; species name
+	dw 100, 80 ; height, weight
+
+	db   "This #MON's"
+	next "impressive vital-"
+	next "ity allows it to"
+	page "live anywhere. It"
+	next "also multiplies"
+	next "very quickly.@"