class Troy::Site

def export_pages(file = nil)
  file = File.expand_path(file) if file
  pages
    .select {|page| file.nil? || page.path == file }
    .each_slice(options[:concurrency]) do |slice|
      threads = slice.map do |page|
        Thread.new do
          page.save
        end
      end
      threads.each(&:join)
    end
end