code: def get_data_files_dir():
      
      if 'data_files' in os.listdir(sys.prefix):
          return os.path.join(sys.prefix, 'data_files')
      else:
          return os.path.join(get_pmag_dir(), 'data_files')
docs: Find directory with data_files (sys.prefix or local PmagPy/data_files)
      and return the path.