def unshift *elements
      elements.each do |element|
        node = LLNode.new(element, @first, nil)
        @last = node if @last.nil?
        @first.previous = node unless @first.nil?
        @first = node
        @size += 1
      end
      self
    end
def unshift *elements
      elements.each do |element|
        node = LLNode.new(element, @first, nil)
        @last = node if @last.nil?
        @first.previous = node unless @first.nil?
        @first = node
        @size += 1
      end
      self
    end
Prepends objects to the front of +self+, moving other elements
 upwards. See also #shift for the opposite effect.