add method config()

[azoyan]

Add config() method that extracts current Config of the file log writer

For example to find out in which directory the log is written:

fn reset_logger(logger: Arc<Mutex<LoggerHandle>>) {
    let logger = logger.lock().unwrap();
    let logger_config = logger.config().unwrap();
    let directory = logger_config.directory(); // we need to know current directory
    let file_spec = FileSpec::default().directory(&directory).basename("basename");

    logger.reset_flw(&FileLogWriter::builder(file_spec)).unwrap();
}

[emabee]

The PR seems to undo a couple of recent changes. Could you please rebase?

[azoyan]

The PR seems to undo a couple of recent changes. Could you please rebase?

Ok. Rebase done and changed files updated.