def lifespan=(lifespan)
      @lifespan = lifespan
      @@lifespans.each_with_index do |span, index|
        if span[0] == lifespan && lifespan != "Forever"
          self.expires = DateTime.now.advance(@@lifespans[index][1])
        end
      end
    end
def lifespan=(lifespan)
      @lifespan = lifespan
      @@lifespans.each_with_index do |span, index|
        if span[0] == lifespan && lifespan != "Forever"
          self.expires = DateTime.now.advance(@@lifespans[index][1])
        end
      end
    end
Setter to convert user's choice of 'A Week', etc. to an actual DateTime