[Feature Request] Return error code when url is not valid

[DopeforHope]

The following command doesn't exit with an error code.

> python3 webpage2html.py --errorpage -s https://www.wivfwfekipedia.org 
[ WARN ] ??? - https://www.wivfwfekipedia.org HTTPSConnectionPool(host='www.wivfwfekipedia.org', port=443): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x7f60a48fbba8>: Failed to establish a new connection: [Errno -2] Name or service not known',))
>

[zTrix]

Seems to be a network connectivity issue? Name or service not known probably indicates that DNS is not working as expected.