changed arg parsing, with comments

[GParks]

I want to add this ("new") parsing func. for cmd-line args, and I think it's general a good, generic expansion

[mapitman]

Thanks for the PR, @GParks! The mdview file.md -o out.html problem you hit is fixed on main now (#67, PR #76). It uses the same approach as yours, with -- handling and tests added.

Other changes have landed since, so your diff would conflict. I'm going to close this one, but I appreciate you taking the time to contribute.