* adjust HttpRequest ctor signature: ctor(StreamReader) -> ctor(Stream)
* create StreamReader for use in HttpRequest ctor
* remove property HttpRequest.Raw
* adjust HttpRequest.ParseMultipartFormData signature: (string, string) -> (Stream, string)
* remove StreamReader creation from HttpServer's request handler (passes MemoryStream directly to HttpRequest)
* change "* remove StreamReader creation from HttpServer's request handler (passes MemoryStream directly to HttpRequest)" from last commit didn't get committed, this adds it
add charset->Encoding map