IoRing support for windows

IoRing is a new windows api.

[Thomasdezeeuw]

Duplicate of #1591. Basically it's a maybe for Mio v2, otherwise you can look at https://github.com/Thomasdezeeuw/a10 which works on Linux currently.

[dlight]

Note that I/O ring is a Windows API, while io_uring is a Linux API. A10 is a crate for Linux io_uring, not Windows I/O rings.

Here is a comparison between the two APIs.

So, this is not a duplicate I think.

[Thomasdezeeuw]

I'll reopen, but it think the design is fairly similar between Windows' I/O ring and Linux's io_uring. Neither of which is compatible with Mio's current design.