Add doc for modules for --list

[Spatenheinz]

PR for #2194.

[casey]

Nice! Two things:

• This should have a test which shows that doc comments are printed, and that they're aligned.
• Since Subcommand::format_doc is only used inside of Subcommand::list_module, I would put it inside that function.

[Spatenheinz]

Ok I am a bit unsure why it shows other commits than mine as well. Maybe it is because I have rebased my fork in the meanwhile?

I think it should follow your requirements.
I also changed /bin/echo to /usr/bin/env echo in tests/functions as some of them where failing on for me on NixOS. using /usr/bin/env should be more universal. I just replaced all occurences of it for consistency. Let me know if you disagree.

[casey]

Looks good to me! I made some minor changes, mainly alphabetizing argument lists (when they get long enough, I just sort the argument by name instead of having some semantic order) and un-hiding the doc from the JSON serialization, and fixing the JSON tests.

The extra commits are expected, if you rebase onto a new version of master, you'll see those extra commits, but I ultimately always squash merge, so they get squashed away when they get merged to master.