Keep unique exit codes

We use exit(1) whenever we want to show an error. We need to consider throwing unique and meaning full error codes ( exit(10), exit(20), exit(21)). 20 and 21 here denote that they are part of the same function

changed the description

That's a good idea.

We could use unique integers, and create a table of the integers together with a short explanation of the error scenario somewhere. Perhaps in the developer.rst file?

mentioned in merge request !94 (merged)

closed with merge request !94 (merged)

mentioned in commit cf3b0225