Make rustic compile on Windows

[aawsome]

ToDos - to make rustic compile on windows :

• remove dependency on users crate for windows
• use hack for SIGPIPE in main.rs only on unix systems
• adapt backend/ignore.rs
• adapt backend/local.rs
• make a own version of converting windows filenames to/from String in backend/node.rs
• consollidate the quick hack in cmd/restore.rs:528 with functionality within ignore.rs or local.rs