Because this API only errors when write!() errors occur, we can return
the exit code as an error here.
This way the user of the API can immediately exit if there was an IO
error, but the API automatically takes care of the right return value,
returning (exiting) with zero (0) if there was an "Broken pipe" error
and with one (1) otherwise, which is the expected behaviour here.
All calls to that API were changed accordingly.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
This merge solved a _LOT_ of conflicts and was a rather complicated one,
as parts of the conflict-resolution involved rewriting of half the
stuff.
This merge commit fixes all the things so a `cargo check --all`
succeeds, but I did not yet check whether tests run without failure.
