ruby-strptimeの履歴
hoge = '2012/03/20' dt = Date.strptime(hoge, '%Y/%m/%d') => Tue, 20 Mar 2012
hoge = '2012/03/20 12:45' dt = DateTime.strptime(hoge, '%Y/%m/%d %I:%M') => Tue, 20 Mar 2012 12:45:00 +0000
hoge = '2012/03/20' dt = Date.strptime(hoge, '%Y/%m/%d') => Tue, 20 Mar 2012
hoge = '2012/03/20 12:45' dt = DateTime.strptime(hoge, '%Y/%m/%d %I:%M') => Tue, 20 Mar 2012 12:45:00 +0000