A couple of minor fixes

[gpiero]

• Exit with EX_OK instead of EX_USAGE if clingon.help.flag is set
• Do not print command's short description if it's not set

[dnaeon]

Hey @gpiero ,

Could you please rebase your branch against the latest master branch, so that the merge commit is not part of the PR?

Thanks!

[gpiero]

Sure, sorry for the mess.

[dnaeon]

Hey @gpiero ,

Merged, thanks!