add support for loading custom axis labels from csv

    const Expr* expr,

    Formatter* formatter) {

  std::vector<std::string> values;

  if (expr && expr_is_list(expr)) {

    if (auto rc = data_load_strings(expr, &values); !rc) {

      return rc;

    }

  } else {

    for (; expr; expr = expr_next(expr)) {

      values.emplace_back(expr_get_value(expr));

    }

  }

  *formatter = format_custom(values);

  return OK;