Weekdate2date


 * week date to date
 * ISO-8601
 * test set
 * 2004-W53-6 → 2005-01-01
 * 2004-W53-7 → 2005-01-02
 * 2005-W52-6 → 2005-12-31
 * 2007-W01-1 → 2007-01-01
 * 2007-W52-7 → 2007-12-30
 * 2008-W01-1 → 2007-12-31
 * 2008-W01-2 → 2008-01-01
 * 2009-W01-1 → 2008-12-29
 * 2009-W01-3 → 2008-12-31
 * 2009-W01-4 → 2009-01-01
 * 2009-W53-4 → 2009-12-31
 * 2009-W53-7 → 2010-01-03