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/porygon2.asm

@@ -0,0 +1,10 @@
+; Porygon2PokedexEntry: ; 0x1d110c
+	db "VIRTUAL@" ; species name
+	dw 200, 720 ; height, weight
+
+	db   "This manmade"
+	next "#MON evolved"
+	next "from the latest"
+	page "technology. It"
+	next "may have unprog-"
+	next "rammed reactions.@"