2004-10-05 R2.0 R https://stat.ethz.ch/pipermail/r-announce/2004/000792.html R2.0.0の新機能・変更 http://www.okada.jp.org/RWiki/?%A3%D22.0.0%A4%CE%BF%B7%B5%A1%C7%BD%A1%A6%CA%D1%B9%B9