hyperium
Introduce QUIC traits
This adds initial support for QUIC to hyper, a prerequisite for HTTP/3 support.
This adds a new module, hyper::rt::quic, and new traits which largely match what was originally proposed for the h3 crate. The idea is similar to the other transport traits in hyper::rt, which is that a user can describe to hyper how their QUIC implementation works, and then hyper will be able to use that for HTTP/3.
While the h3 crate has drifted some from the original proposal, I wasn't sure the additional complexity that had been added was necessary to expose at the hyper level. If during the implementation process it proves we do need it, we can make the change.
These traits are put behind a cfg(hyper_unstable_quic) flag, until they are stabilized.
This should likely stay as a PR proposal until a separate PR is ready to merge that integrates these traits with HTTP/3 glue in hyper::proto::h3.
Please keep comments to implementation details.
cc #1818
