The file used for logging.
The LogLevel for the FileLogger. By default the LogLevel for FileLogger is LogLevel.all.
if yes and fn contains a folder name, this folder will be created.
auto file = File("logFile.log", "w"); auto l1 = new FileLogger(file); auto l2 = new FileLogger(file, LogLevel.fatal);
A constructor for the FileLogger Logger that takes a reference to a File.
The File passed must be open for all the log call to the FileLogger. If the File gets closed, using the FileLogger for logging will result in undefined behaviour.