code: function loadConfigCore(configItem) {
    if (typeof configItem === "string") {
      configItem = fs.readFileSync(configItem, "utf8");
    } else if (typeof configItem === "object") {
      // do nothing
    } else {
      throw new Error("Unexpected config item type.");
    }
  
    return configItem;
  }
docs: Load config core function, from object or local config file
  @param {Object|String} configItem - Config object or file path
  @returns {Object} Kotori config
  @private