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/magikarp.asm

@@ -0,0 +1,10 @@
+; MagikarpPokedexEntry: ; 0x1cc000
+	db "FISH@" ; species name
+	dw 211, 220 ; height, weight
+
+	db   "This weak and"
+	next "pathetic #MON"
+	next "gets easily pushed"
+	page "along rivers when"
+	next "there are strong"
+	next "currents.@"