WinIO

@Mistuke I'm trying to understand whether or not I can support WinIO by myself.

I gathered patches so far: https://github.com/kazu-yamamoto/network/commits/win-io/

The key change is the `Socket` type:

```
#if defined(mingw32_HOST_OS)
type CSocket = SOCKET
#else
type CSocket = CInt
#endif

data Socket = Socket (IORef CSocket) CSocket {- for Show -}
```

If we can pass `CSocket` to `threadWaitRead`/`threadWaitWrite`, I guess most integration is done.

In4bf542bf1cdf2fa468457fc0af21333478293476 of GHC gitlab tree, you added the following:

```
threadWaitRead :: BHandle a => a -> IO ()
```

This is really promising but you reverted it in b3ad2a54bf775e1ca110b501894891d4ccff3d8f.
So, I cannot find any ways to pass `CSocket` to these functions.
Would you suggest how we can achieve the purpose?