Just some papercuts I noticed while trying out the CLI:

• args.run() is an unfortunate place to do argument validation; can just as well do it while parsing.
• I messed up my bbox the first time around and got an unhelpful error. No more!
• It's useful to be able to always choose to save the Overpass data to a file, instead of only when happening to use --debug, so that's now a thing (--save-json-file).