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

waybackpy/cli.py

@@ -29,6 +29,8 @@ def _save(obj):
                     version=__version__, header=header
                 )
             )
+        if "URL cannot be archived by wayback machine as it is a redirect" in e:
+            return ("URL cannot be archived by wayback machine as it is a redirect")
         raise WaybackError(err)