The "rktio" library (for "Racket I/O") is a layer just above the OS
layer to provide a portable interface to filesystem, networking, etc.
facilities.

The library is meant to be

 * easily embeddable;

 * always non-blocking;

 * independent of global state, so that it works with or without
   threads;

 * require no C preprocessor conditionals in client code; and

 * easily callable though a FFI.

Many such libraries exist already. This one happens to have exactly
the things that a Racket implementation needs.

See "rktio.h" for the API.

If you add new things to "rktio.h", then run `make -f Mf-rktio` to
generate "rktio.rktl", "rktio.inc", and "rktio.def". (That requires a
`racket` executable in your `PATH`.) Those derived files supply glue
for Racket CS and Racket BC to use rktio functionality.