Merge pull request #1 from openscad/master

update from main
Changed exit codes to 0 and added help description to help menu #1028
Merge branch 'master' of https://github.com/jgelderloos/openscad
Merge branch 'master' of git://github.com/jgelderloos/openscad
#1028 Adjusted return values for errors
Merge remote-tracking branch 'origin/master' into jgelderloos-master
Merge branch 'master' of github.com:openscad/openscad
Merge branch 'jgelderloos-master'