Add sample file for signed wordlists.

This sample wordlist contains only 2 entries but is
cryptographically signed. We use it to make sure we can also
handle signed wordlists.

tests/sample_signed_wordlist.asc

+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA512
+
+foo
+bar
+-----BEGIN PGP SIGNATURE-----
+Version: GnuPG v1
+
+iJwEAQEKAAYFAlWwtFAACgkQ+5ktCoLaPzT6dAP/YOac16xtJ0oDtVmouhYgXY6J
+A6jyR8nW2tn+5NksBrXgy/OLgwD2ljlZuhPDarancD8e2tkoPKr0Diuk4oTSe4m7
+sAH4PvMPvUw9Rn0gfx20QMbTrLqQ8I4I7cw6u3RIqilB+p80V+SWFApvoHC6l0ZU
+EkreblTdKgoQ2CzP0RM=
+=3BRe
+-----END PGP SIGNATURE-----