docs: def build_CLASS(prefix):
      """
      Function to dowwnload CLASS from github and and build the library
      """
      # latest class version and download link
      args = (package_basedir, package_basedir, CLASS_VERSION, os.path.abspath(prefix))
      command = 'sh %s/depends/install_class.sh %s %s %s' %args
  
      ret = os.system(command)
      if ret != 0:
          raise ValueError("could not build CLASS v%s" %CLASS_VERSION)