Add MIME support

- Wrap encrypted mails into a mime structure
- Add 'protected headers'

src/config.rs

@@ -40,7 +40,7 @@ impl HuskConfig {
                 Err(HuskError::ConfigFileOpenError(format!(
                     "{} - {}",
                     path,
-                    e.to_string())).into())
+                    e)).into())
             }
         }
     }