Add a no-return attribute

Any function that has the NoReturn attribute may close the other side of
the socket without causing an error, and will perform exit(0) whenever
that happens.
Do not mix raw and stdio I/O

This was causing some large outputs to be racy since the large 1024-byte
chunks were written directly into the file descriptor and shorter chunks
were written into the stdio buffer, which made the output come in a
weird order. This probably fixes #11.
Version 1.4.0

* Added the NoReturn attribute for functions that may call exit().
* Lots of improvements over the Windows run.bat

Bugfixes since 1.3.0:

* Better buffering of Pascal I/O, fixing some RTE.
* Large outputs no longer confuse the runner program.