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/squirtle.asm

@@ -0,0 +1,10 @@
+; SquirtlePokedexEntry: ; 0x181926
+	db "TINYTURTLE@" ; species name
+	dw 108, 200 ; height, weight
+
+	db   "When it feels"
+	next "threatened, it"
+	next "draws its legs"
+	page "inside its shell"
+	next "and sprays water"
+	next "from its mouth.@"