docs: def merge_files(sources, destination):
      """Copy content of multiple files into a single file.
  
      :param list(str) sources: source file names (paths)
      :param str destination: destination file name (path)
      :return:
      """
  
      with open(destination, 'w') as hout:
          for f in sources:
              if os.path.exists(f):
                  with open(f) as hin:
                      shutil.copyfileobj(hin, hout)
              else:
                  logger.warning('File is missing: {}'.format(f))