Add record index with key _index

lib/tallty_import_export/export.rb

@@ -81,12 +81,12 @@ module TalltyImportExport
         sheet.add_row headers.map{|header| header[:name]}, style: title2, height: 39
 
         each_method = records.is_a?(Array) ? :each : :each
-        records.send(each_method) do |record|
+        records.send(each_method).with_index do |record, index|
           row = []
-          headers.each{ |header| row.push(handle_data(record, header)) }
+          headers.each{ |header| row.push(handle_data(record, header, index)) }
           sheet.add_row row, style: title3, height: @row_height, types: headers.map{|header| header[:format]}
         end
-        sheet.column_widths *headers.map{|header| header[:width] || @width}
+        sheet.column_widths(*headers.map{|header| header[:width] || @width})
       end
     end
 
@@ -113,9 +113,11 @@ module TalltyImportExport
     end
 
     # 处理一个记录的数据
-    def handle_data record, header
+    def handle_data record, header, index: 0
       data =
-        if header[:method].present?
+        if header[:key] == '_index'
+          index + 1
+        elsif header[:method].present?
           send(header[:method], record, header)
         elsif header[:chain].present?
           header[:chain].reduce(record) do |obj, method|