add another method to get html document

type.go

@@ -32,6 +32,14 @@ func NewDocument(url string) (d *Document, e error) {
 	if e != nil {
 		return
 	}
+	return NewDocumentWithHttpResponse(res)
+}
+
+// NewDocumentWithHttpResponse() is another Document constructor that takes a http resonse as argument.
+// If you want to get some page which need be authorized,this method may be helpful
+// It loads the specified document, parses it, and stores the root Document
+// node, ready to be manipulated.
+func NewDocumentWithHttpResponse(res *http.Response) (d *Document, e error) {
 	defer res.Body.Close()
 
 	// Parse the HTML into nodes