Some commands cause a traceback when given no args

[vesche]

This is caused by nargs='?' which is fine... Just need to check for required args in run.

• base64
• xxd

Need to be fixed.

For example in curl to avoid this problem:

def run(self):
    args = self.get_args()
    url = args['url']

    if not url:
        print("Error: No URL specified.")
        return