message: writer mode and directory
diff: @@ -57,7 +57,10 @@ fn run() -> Result<(), Error> {
  solver.add_logger(ArgminSlogLogger::term());
  // Attach a writer
  - solver.add_writer(WriteToFile::new());
  + solver.add_writer(WriteToFile::new("params"));
  +
  + // Set how often parameter should be saved
  + solver.set_writer_mode(WriterMode::Every(3));
  // Run solver
  solver.run()?;
  