post格式
{"layout"=>"post", "title"=>"Hello world!", "date"=>2014-09-25 01:26:48 +0800, "categories"=>["unknow"], "url"=>"/unknow/2014/09/25/hello-world.html", "dir"=>"/unknow/2014/09/25", "id"=>"/unknow/2014/09/25/hello-world", "next"=>nil, "previous"=>, "tags"=>[], "path"=>"_posts/2014-09-24-hello-world.markdown", "content"=>"