def tag(name)
      tags.find {|tag| tag.tag_name.to_s == name.to_s }
    end
def tag(name)
      tags.find {|tag| tag.tag_name.to_s == name.to_s }
    end
Convenience method to return the first tag
 object in the list of tag objects of that name

 @example
   doc = Docstring.new("@return zero when nil")
   doc.tag(:return).text  # => "zero when nil"

 @param [#to_s] name the tag name to return data for
 @return [Tags::Tag] the first tag in the list of {#tags}