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/ekans.asm

@@ -0,0 +1,10 @@
+; EkansPokedexEntry: ; 0x181fd4
+	db "SNAKE@" ; species name
+	dw 607, 150 ; height, weight
+
+	db   "It flutters the"
+	next "tip of its tongue"
+	next "to seek out the"
+	page "scent of prey,"
+	next "then swallows the"
+	next "prey whole.@"