Use CURLOPT_WRITEFUNCTION to check the response code and content type (only allow HTML).
Also extract the title and charset during downloading chunk of data, and stop it when everything has been extracted.
Closes#579
* `get_http_url()` renamed to `get_http_response()`.
* Use the same HTTP context to retrieve response headers and content.
* Follow HTTP 301 and 302 redirections to retrieve the title (default max 3 redirections).
* Add `LinkUtils` to extract titles and charset.
* Try to retrieve charset from HTTP headers first (new), then HTML content.
* Use mb_string to re-encode title if necessary.
