support .torrent urls with gzip/deflate response

Some servers always return a gzip response even when clients don't send `accept-encoding: gzip`. This PR adds support for such misbehaved servers, and also always requests gzipped responses.

Using the `simple-get` module (https://npmjs.org/package/simple-get), the lightest possible wrapper on top of core http, but also supporting:

- follow redirects
- automatically handle gzip/deflate responses
- supports HTTPS