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/raikou.asm

@@ -0,0 +1,10 @@
+; RaikouPokedexEntry: ; 0x1d156b
+	db "THUNDER@" ; species name
+	dw 603, 3920 ; height, weight
+
+	db   "This rough #MON"
+	next "stores energy"
+	next "inside its body,"
+	page "then sweeps across"
+	next "the land, shooting"
+	next "off electricity.@"