docs: def start_log(level=logging.DEBUG, filename=None):
      """start the logger for the run
  
      Parameters
      ----------
      level : int, optional
          logging.DEBUG, logging.INFO etc. for the log level (between 0-50).
      filename : str, optional
        name of the filename to save the log to or
        None (default) to use deblur.log.TIMESTAMP
      """
      if filename is None:
          tstr = time.ctime()
          tstr = tstr.replace(' ', '.')
          tstr = tstr.replace(':', '.')
          filename = 'deblur.log.%s' % tstr
      logging.basicConfig(filename=filename, level=level,
                          format='%(levelname)s(%(thread)d)'
                          '%(asctime)s:%(message)s')
      logger = logging.getLogger(__name__)
      logger.info('*************************')
      logger.info('deblurring started')