code: function(settingSpec) {
          var setting = new Setting(settingSpec, this);
          this._settings[setting.name] = setting;
          this._settingNames.push(setting.name);
          this._settingNames.sort();
      }
docs: Function to add to the list of available settings.
  <p>Example usage:
  <pre>
  var settings = plugins.catalog.getObject('settings');
  settings.addSetting({
  name: 'tabsize', // For use in settings.get('X')
  type: 'number',  // To allow value checking.
  defaultValue: 4  // Default value for use when none is directly set
  });
  </pre>
  @param {object} settingSpec Object containing name/type/defaultValue members.