fd: synchronous and asynchronous file descriptors
fd implements an API identical to lua's file object but with support for async operations following the lib/lap protocol.
It also contains a few simple file-backed data structures (fd.VFile and fd.LLFile).

Mod fd

filedescriptor: direct control of filedescriptors. async operations support the LAP (see lib/lap) protocol.
Can override default `io` module for global async mode. Functions

• fn isTrunc(mode) -> bool
  Given a string mode, return whether the file will be truncated.
• fn isCreate(mode)
  Given a string mode, return whether the file will be created if it doesn't exist.
• fn newFD
• fn newFDT
• fn finishRunning(fd, kind, ...)
• fn modifiedEq(fs1, fs2)
  return whether two fstat's have equal modification times FIXME: move this to civix
• fn openWith(openFn, path, mode)
• fn openFD(...) -> M.openWith(S.openFD, ...)
• fn openFDT(...) -> M.openWith(S.openFDT, ...)
• fn open(...)
• fn close()
• fn tmpfileFn(sysFn)
• fn tmpfile() -> M.tmpfileFn(S.tmpFD)
• fn read(...)
• fn lines(path, mode)
• fn write(...) -> M.output():write(...)
• fn openFileno(fileno)
• fn input() -> M.stdin
• fn output() -> M.stdout
• fn flush() -> M.output():flush()
• fn type(fd)
• fn fileno(fd)
• fn ftype(f)
• fn isatty(fd)
• fn ioStd()
• fn ioSync()
• fn ioAsync()