Because we need to catch errors that are caused by a borken pipe when
writing to stdout (for example), this patch changes the interface of the
Viewer trait to return an error enum that can be used to check whether
an IO error happened.
The calling code can then decide whether to ignore a broken pipe error
or whether to handle it properly.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
This patch removes unused crate imports reported by newer rust versions.
Some crates were only required for tests, some only for tests with
macro_import - these things were fixed with feature gates.
