* 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.
It had the downside of running all the comptime blocks and resolving
all the usingnamespaces of each system, when just trying to discover if
the current system is a particular one.
For Darwin, where it's nice to use `std.Target.current.isDarwin()`, this
demonstrates the utility that #425 would provide.
