added RedirectSaveError - for failed saves if the URL is a permanent … (#93)

* added RedirectSaveError - for failed saves if the URL is a permanent redirect.

* check if url is redirect before throwing exceptions, res.url is the redirect url if redirected at all

* update tests and cli errors

tests/test_cli.py

@@ -29,7 +29,7 @@ def test_save():
         get=None,
     )
     reply = cli.args_handler(args)
-    assert "could happen because either your waybackpy" in str(reply)
+    assert "could happen because either your waybackpy" or "cannot be archived by wayback machine as it is a redirect" in str(reply)
 
 
 def test_json():