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/magneton.asm

@@ -0,0 +1,10 @@
+; MagnetonPokedexEntry: ; 0x1b870a
+	db "MAGNET@" ; species name
+	dw 303, 1320 ; height, weight
+
+	db   "When many"
+	next "MAGNETON gather"
+	next "together, the"
+	page "resulting magnetic"
+	next "storm disrupts"
+	next "radio waves.@"