feat(transport): Add Router::into_service

[tjtelan]

Motivation

Coincidentally I was going to open an issue for this after spending some time on my own trying to accomplish this, but #410 was on the first page.

I wanted to help merge #272 since it appeared to be slightly stalled. I have a need for the functionality of running an HTTP server and a gRPC server with multiple services on the same port.

Solution

The major work appeared to be complete and was appeared to be an acceptable implementation. The finishing code was actually provided in #272 (comment) so I just barely provided work. It was a successful group effort overall.

I rebased the PR branch w/ respect to the original author @cthulhua (with a minor change the import of futures_util::Future::Either) and moved the service function into the Router impl as per the original feedback.

Testing

Additionally, I added a new example hyper_warp_multiplex, a mix of the hyper_warp and multiplex examples.

• cargo run --bin hyper-warp-multiplex-server
• cargo run --bin hyper-warp-multiplex-client

[cthulhua]

Thanks for taking this over; I’ve had a wild few months and haven’t been able to close this out

[olanod]

I also ran into the need of having the gRPC server alongside a warp HTTP server on the same port(might even need websockets?) and wanted to know how feasible it is and if it would require work only on tonic's side.

[LucioFranco]

Looks great, left some nits on docs, otherwise I think we can merge this! Thanks!

[LucioFranco]

Thanks!