Use HtmlKit tokenizer for HTML5 parsing - #243

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

Dereference of a possibly null reference.

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)

'WebClient.WebClient()' is obsolete: 'WebRequest, HttpWebRequest, ServicePoint, and WebClient are obsolete. Use HttpClient instead.' (https://aka.ms/dotnet-warnings/SYSLIB0014)