Extend link helper, link_to, to add "active" class if link url is to current page. https://github.com/middleman/middleman/issues/303

link_to_active_class.erb

helpers do
  def magic_link_to(link, url, opts={})
    if request.path == link
      opts[:class] = "active"
    end
    link_to(link, url, opts)
  end
end