This is useful for platforms which might want to avoid the cost of
password based key-derivation and have the ability to securely store an
encryption key.
Co-authored-by: Denis Kasak <dkasak@termina.org.uk>
Clippy on nigtly is raising a warning, which is turned into an error
on the CI. It's the [`explicit_auto_deref`
lint](https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref). I
suspect it's a false-positive but I'm not sure. Anyway, to workaround
this and unblock our CI, let's call `DerefMut::deref_mut` manually:
it's clearer anyway.
