docs: def add_features(host_name, client_name, client_pass, feature_names):
      """
      Add a number of numerical features in the client.
  
      Inputs: - host_name: A string containing the address of the machine where the PServer instance is hosted.
              - client_name: The PServer client name.
              - client_pass: The PServer client's password.
              - feature_names: A python list of feature names.
      """
      init_feats = ("&".join(["%s=0"]*len(feature_names))) % tuple(feature_names)
      features_req = construct_request("pers",
                                       client_name,
                                       client_pass,
                                       "addftr",
                                       init_feats)
      send_request(host_name,
                   features_req)