Documentation for method
week assembled from the following types:
(Dateish) method week
Returns a list of two integers: the year, and the week number. This is because at the start or end of a year, the week may actually belong to the other year.
my (, ) = Date.new("2014-12-31").week;say ; # OUTPUT: «2015␤»say ; # OUTPUT: «1␤»say Date.new('2015-01-31').week; # OUTPUT: «(2015 5)␤»