HtmlAgilityPack是一款强大的HTML解析器，并且是完全开源的，
官网：http://html-agility-pack.net/
C# HTML Parser Examples
// From File
var doc = new HtmlDocument();
doc.Load(filePath);
// From String
var doc = new HtmlDocument();
doc.LoadHtml(html);
// From Web
var url = "http://html-agility-pack.net/";
var web = new HtmlWeb();
var doc = web.Load(url);