* add reserved field to match musl struct definition so that
it will work with musl libc.
* add libc getrusage so that it will work with libc
what's not done in this branch is:
* test coverage. See #1629, which should also aim to provide
general test coverage for the std lib.
* rusage struct bits for non-linux operating systems
* Delete `std.net.TmpWinAddr`. I don't think that was ever meant to
be a real thing.
* Delete `std.net.OsAddress`. This abstraction was not helpful.
* Rename `std.net.Address` to `std.net.IpAddress`. It is now an extern
union of IPv4 and IPv6 addresses.
* Move `std.net.parseIp4` and `std.net.parseIp6` to the
`std.net.IpAddress` namespace. They now return `IpAddress` instead of
`u32` and `std.net.Ip6Addr`, which is deleted.
* Add `std.net.IpAddress.parse` which accepts a port and parses either
an IPv4 or IPv6 address.
* Add `std.net.IpAddress.parseExpectingFamily` which additionally
accepts a `family` parameter.
* `std.net.IpAddress.initIp4` and `std.net.IpAddress.initIp6` are
improved to directly take the address fields instead of a weird
in-between type.
* `std.net.IpAddress.port` is renamed to `std.net.IpAddress.getPort`.
* Added `std.net.IpAddress.setPort`.
* `os.sockaddr` struct on all targets is improved to match the
corresponding system struct. Previously I had made it a union of
sockaddr_in, sockaddr_in6, and sockaddr_un. The new abstraction for
this is now `std.net.IpAddress`.
* `os.sockaddr` and related bits are added for Windows.
* `os.sockaddr` and related bits now have the `zero` fields default
to zero initialization, and `len` fields default to the correct size.
This is enough to abstract the differences across targets, and so
no more switch on the target OS is needed in `std.net.IpAddress`.
* Add the missing `os.sockaddr_un` on FreeBSD and NetBSD.
* `std.net.IpAddress.initPosix` now takes a pointer to `os.sockaddr`.
