Support io_uring

[lpereira]

io_uring first appeared in Linux 5.1, and is in heavy development. It is a new async I/O primitive that addresses a lot of issues in the traditional readiness-based I/O model that Unix uses, that significantly reduces latency and increases throughput. This article is a good introduction.

With the advent of fat pipes, saturating a link with the traditional API is becoming increasingly difficult. Switching to something like this should help achieve that goal.