Constructor which opens fileName on disk, using the given mode. Valid mode are 'r' (read), 'w' (write) or 'rw' (read-write). Default is read mode.

If read-write mode, the file will be created if it does not exists. If it exists, it will be positionned at the beginning of the file after opening.

If (and only if) quiet is true, no error will be raised in case of problem opening the file: instead nil will be returned.

The file is opened in ASCII mode by default.