Add hyper integration

[MikailBag]

Solves #1070 without exposing too many APIs

[svenstaro]

This would be great to have. I'm currently trying to integrate Sentry but there's no single future I can call to attach the Hub to via bind_hub() so the integration is very lackluster right now. Also for tracing this would be really nice to have.

[SergioBenitez]

My apologies for coming to this a year and a half later.

I don't think exposing hyper types is the approach we want to take on this one. I think the approach we want to take is one significantly less heavy-handed. Something like:

rocket::build()
    .listen(anything_implementing_listener)

One of the issues with doing this before was configuration. Given the monumental improvements in configuration, I think we can now say that the proper approach here would be to allow the listener to configure itself. The default TCP/TLS listener would read values as it does today, but otherwise the listener can do whatever it wants.