Utilities to create *html.Node from http.Request and http.Response

[MarcusAdriano]

I've used this library a few days ago and I was forced to re-implement in my code LoadURL because my Get request needs customization like custom headers.

Basically there are two new functions:

• LoadHttpResponse: interpret http response like LoadURL, but without make http request;
• LoadRequest: make http request using provided request.

[zhengchun]

Hello, @MarcusAdriano , First, thanks for your contribution. htmlquery package focusing on XPath query. I encourage developer to implement HTTP requests depend on your project instead of LoadURL(). Not plan add the new HTTP handler method for package, sorry.