def pages_linking_to(urls)
      unless urls.is_a?(Array)
        urls = [urls]
        single = true
      end

      urls.map! do |url|
        unless url.is_a?(URI)
          URI(url) rescue nil
        else
          url
        end
      end
      urls.compact

      links = {}
      urls.each { |url| links[url] = [] }
      values.each do |page|
        urls.each { |url| links[url] << page if page.links.include?(url) }
      end

      if single and !links.empty?
        return links[urls.first]
      else
        return links
      end
    end
def pages_linking_to(urls)
      unless urls.is_a?(Array)
        urls = [urls]
        single = true
      end

      urls.map! do |url|
        unless url.is_a?(URI)
          URI(url) rescue nil
        else
          url
        end
      end
      urls.compact

      links = {}
      urls.each { |url| links[url] = [] }
      values.each do |page|
        urls.each { |url| links[url] << page if page.links.include?(url) }
      end

      if single and !links.empty?
        return links[urls.first]
      else
        return links
      end
    end
If given a single URL (as a String or URI), returns an Array of Pages which link to that URL
 If given an Array of URLs, returns a Hash (URI => [Page, Page...]) of Pages linking to those URLs