def links_to_follow(page)
      links = @focus_crawl_block ? @focus_crawl_block.call(page) : page.links
      links.select { |link| visit_link?(link, page) }.map { |link| link.dup }
    end
def links_to_follow(page)
      links = @focus_crawl_block ? @focus_crawl_block.call(page) : page.links
      links.select { |link| visit_link?(link, page) }.map { |link| link.dup }
    end
Return an Array of links to follow from the given page.
 Based on whether or not the link has already been crawled,
 and the block given to focus_crawl()