uds

• Remove tokio support. Because 0.2 is not much used at this point. 1.* support might be implemented later.
• Remove mio 0.6, mio-uds & mio 0.7 support. To simplify code and reduce combinations of features to test.
  The feature for mio 0.8 support remains "mio_08": "mio" is reserved for mio 1.0.

• Don't return truncatedness from UnixSeqpacketConn and tokio::UnixSeqpacketConns recv() and peek() methods. For consistency with the return types of similar methods on stream and datagram types.
  Use recv_vectored() with empty fd buffer if you want to know whether the packet was truncated.
• Remove default impl of UnixDatagramExt::bind_unix_addr(), and remove Sized bound on the trait.
• Stop quoting Unnamed in UnixSocketaddr's Debug impl.
• Add mio_08 feature, for using this library with mio 0.8.
• Require Rust 1.63. (Mainly to make CI pass, so older versions will likely work.)

Out-of-bounds writes could have happened if sending both credentials
and file descriptors, but sending credetials is not exposed,
so that code is unreachable. Puh.

• Add take_error() and into_nonblocking() to tokio seqpacket types.
• Implement AsRef to nonblocking variants for tokio seqpacket types.

• Add send_vectored() and recv_vectored() to ::tokio::UnixSeqpacketConn.
• Add peek() and peek_vectored() to ::tokio::UnixSeqpacketConn.
• Add send_fds() and recv_fds() to ::tokio::UnixSeqpacketConn.
• Implement AsRawfd and IntoRawFd for tokio seqpacket types.
• Add fallible from_raw_fd() to tokio seqpacket types.
• Add from_nonblocking() to ::tokio::UnixSeqpacketListener.
• Fix initial_peer_credentials() impl for Illumos & Solaris writing to stdout.

• Implement peer credentials on NetBSD and DragonFly BSD.
• Add initial_peer_selinux_context().
• Add initial_peer_credentials() to ::tokio::UnixSeqpacketConn.
• Add bind_addr() and local_addr() to ::tokio::UnixSeqpacketListener.
• Add connect_addr(), connect_from_addr(), local_addr() and peer_addr() to ::tokio::UnixSeqpacketConn.

• Add send_to_unix_addr(), recv_from_unix_addr(), peek_from_unix_addr() and vectored variants to UnixDatagramExt.
• Add UnixDatagramExt::bind_unix_addr(). (with a fallback default impl that creates a nonblocking socket)
• Add as_pathname() and as_abstract() to UnixSocketAddr.
• Add name() to UnixSocketAddr and rename UnixSocketAddrRef to AddrName, with a type alias for backwards compatibility.
• Add from_raw_bytes() and as_raw_bytes() to UnixSocketAddr.
• List DragonFly BSD as supported after testing on it.

• Compile on 64-bit Android (#4).
• Support OpenBSD (including peer credentials).
• Fix UnixDatagramExt::recv_fds_from() always returning unnamed adress.
• Fix UnixSocketAddr::as_ref() and its Debug impl misrepresenting some unnamed addresses as abstract on operating systems that don't have abstract addresses.
• Fix UnixSocketAddr::as_ref() and its Debug impl having trailing NULs in paths in rare cases. (this has only happened on OpenBSD so far).
• Avoid invoking accept4() on x86 Android (based on mio #1445).

• Add timeout methods to blocking seqpacket types.
• Add take_error() to all seqpacket types.
• Add peek() and peek_vectored() to seqpacket connection types.
• Remove outdated WiP section of README saying NetBSD and Illumos aren't supported.

• Require Rust 1.39.
• Add mio 0.7 support, behind optional feature mio_07.
  (mio 0.6 is still supported and enabled with mio feature.)
• Add tokio seqpacket types, behind optional feature tokio. (by @jmagnuson).
• Add shutdown() to seqpacket connection types (by @jmagnuson).
• Fix creating sockets failing on Illumos & Solaris. (This crate was setting close-on-exec in an unsupported way.)
• Support peer credentials on Illumos / Solaris.
• Enable close-on-exec and non-blocking mode atomically on all OSes where prossible.
  (with SOCK_CLOEXEC, SOCK_NONBLOCK and accept4())
  The only place missing these are macOS (and anything else by Apple).
• Mark NetBSD and Illumos as supported.

• Rename UnixSocketAddr::unspecified() to new_unspecified().
• Add peer_credentials().
• Support macOS and FreeBSD.

• Add UnixSocketAddr to support abstract addresses.
• Add seqpacket types.
• Add extension traits to support FD passing (and to create and accept UnixSocketAddr)