With this patch we move the codebase to Rust-2018.
The diff was generated by executing
cargo fix --all --all-features --edition
on the codebase.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
We create a sha1 over the path of the file and the Message-ID of the
mail itself.
The file name is not constant with mail files, because flags are encoded
in the filename. The path is also not constant with mail files, because
they can be moved between boxes.
This approach is not yet the best one, but better than before.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
