Minor Tweaks

[alphillips-lab]

Hey!

I was planning to use this script for writeups, and made some minor tweaks. In case you'd like them as well, I've changed the following:

• Switched argument parsing to argparse
• Added a --update flag, so that only new challenges are downloaded if set
• Added a -v flag for setting the loglevel
• Added a little more error handling
• Changed the logging in a bit of a crude way, but now there is only a single progress bar for file downloads and log messages are sent under it.

No need to accept any of these changes. I just figured I'd PR them in case you want them as well. Thanks for the work on this :-)