html解析器：Html Agility Pack

去掉注释、样式、和js代码:

foreach(var script in doc.DocumentNode.Descendants("script").ToArray())
    script.Remove();
foreach(var style in doc.DocumentNode.Descendants("style").ToArray())
    style.Remove();

foreach (var comment in doc.DocumentNode.SelectNodes("//comment()").ToArray())
    comment.Remove();//新增的代码