* delete the std/event/net directory
* `std.event.Loop.waitUntilFdReadable` and related functions
no longer have possibility of failure. On Linux, they fall
back to poll() and then fall back to sleep().
* add some missing `noasync` decorations in `std.event.Loop`
* redo the `std.net.Server` API. it's quite nice now, but
shutdown does not work cleanly. There is a race condition with
close() that I am actively working on.
* move `std.io.OutStream` to its own file to match `std.io.InStream`.
I started working on making `write` integrated with evented I/O,
but it got tricky so I backed off and filed #3557. However
I did integrate `std.os.writev` and `std.os.pwritev` with evented I/O.
* add `std.Target.stack_align`
* move networking tests to `lib/std/net/test.zig`
* add `std.net.tcpConnectToHost` and `std.net.tcpConnectToAddress`.
* rename `error.UnknownName` to `error.UnknownHostName` within the
context of DNS resolution.
* add `std.os.readv`, which is integrated with evented I/O.
* `std.os.preadv`, is now integrated with evented I/O.
* `std.os.accept4` now asserts that ENOTSOCK and EOPNOTSUPP never
occur (misuse of API), instead of returning errors.
* `std.os.connect` is now integrated with evented I/O.
`std.os.connect_async` is gone. Just use `std.os.connect`.
* fix false positive dependency loop regarding async function frames
* add more compile notes to help when dependency loops occur
in determining whether a function is async.
* ir: change an assert to ir_assert to make it easier to find
workarounds for when such an assert is triggered. In this case
it was trying to parse an IPv4 address at comptime.
