0.19:
  add io_socketpair
  add io_passfd and io_receivefd (and test/fdpassing.c)
  io_trywrite and io_waitwrite not ignore SIGPIPE
  add man pages for libio, safemult
  fix possible signal race in io_tryread and io_trywrite (Scott Lamb)
  fix byte_rchr return value (Marcus Winkler)
  fix bug in mmap code path of io_sendfile (David Leadbeater)