Might be used when tracker is behind reverse proxy and one of provided
addresses in `real_ip_header` is private/local address.
Additional changes:
* check if provided address is not multicast/broadcast
* configure `http.Server.ReadHeaderTimeout` with `http.ReadTimeout` to mitigate Slowloris
* update dependencies
* minor docs fixes
* add multiple addresses in request structures and frontend parsers
* move per-ip peer fetch/store from storage to internal hooks
* fetch/store both v1 and v2 info hashes
Lawrence, Rendall