%task14-1 - Added solution/array_extansion.rb
%task14-2 - Added method sum
%task14-3 - Need to init 'res' argument
%task14-4 - Fixed sum method
%task14-5 - Added square method
%task14-5 - Fixed square method - need to use .map method
%task14-6 - Fixed square! method - need to use .map method