def field(*fields, export_only: false)
      @config.fields += fields.map(&:to_sym)
      @config.fields.uniq!

      if export_only
        @config.export_only_fields += fields.map(&:to_sym)
        @config.export_only_fields.uniq!
      end

      nil
    end
def field(*fields, export_only: false)
      @config.fields += fields.map(&:to_sym)
      @config.fields.uniq!

      if export_only
        @config.export_only_fields += fields.map(&:to_sym)
        @config.export_only_fields.uniq!
      end

      nil
    end
Add one or many fields to the csv format.

 If options are passed, they apply to all given fields.