- support for writev(2)
- perhaps move 1024-buffer of writef into sa_t and make adjustable
- sa_buffer(sa, <which>, size)
  SA_BUFFER_UREAD
  SA_BUFFER_UWRITE
  SA_BUFFER_KREAD
  SA_BUFFER_KWRITE
  SA_BUFFER_WRITEF
- full test suite for whole API
  - inet://0.0.0.0:0 -> inet://0.0.0.0:514
  - inet://127.0.0.1:514 -> inet://127.0.0.1:514
  - inet://localhost:syslog#udp -> inet://127.0.0.1:514
  - inet://localhost:smtp -> inet://127.0.0.1:25
  - unix:/tmp/socket -> unix:/tmp/socket
- use sa_errorinfo() internally