If the contents of a cell is a URL and does not include a formula, use the HYPERLINK formula to make it clickable.

This also gets around the 65,530 hyperlinks per Worksheet limit in Excel as these `HYPERLINK` formulas do not contribute to that count.

Related to #475.

Author: joshuapinter

lib/rubyXL/worksheet.rb

@@ -57,6 +57,9 @@ def add_cell(row_index = 0, column_index = 0, data = '', formula = nil, overwrit
             end
             c.raw_value = data
             c.datatype = RubyXL::DataType::RAW_STRING
+            if data.match?( URI::DEFAULT_PARSER.make_regexp ) # If content is a URL then use the HYPERLINK formula to make it clickable.
+              c.formula = RubyXL::Formula.new(:expression => %(HYPERLINK("#{ data }")))
+            end
           when RubyXL::RichText then
             if data.to_s.length > TEXT_LENGTH_LIMIT_IN_CELL
               raise ArgumentError, "The maximum length of cell contents (text) is #{TEXT_LENGTH_LIMIT_IN_CELL} characters"