gem - smarter csv

https://github.com/tilo/smarter_csv

invalid byte sequence in UTF-8

rubyエンコーディングに詳しいblog
http://tmtms.hatenablog.com/entry/20120812/ruby_encoding

encoding bug関連コメント
http://blog.livedoor.jp/sonots/archives/23652294.html

from Shift_JIS to UTF-8

http://d.hatena.ne.jp/temita/20130530/1369921154

CSVの読み込みとメモリー

https://www.sitepoint.com/guide-ruby-csv-library-part-2/