Add support for milliseconds timeout

Hey!

According to the PHPDoc, the timeout can accept a float so, this PR adds support for milliseconds timeout. Basically, `CURLOPT_TIMEOUT_MS` has been introduced in curl 7.16.2 so, if it is defined, it is better to rely on it as it is more precise otherwise we rely on `CURLOPT_TIMEOUT` as it is currently.
IMO, it does not matter. curl uses a `long` type in his underlying c++ library. So, PHP will automatically cast it to integer before passing it. It is also the problem with `CULROPT_TIMEOUT` as when we pass `1.1`, it is automatically casted to `1`.