withTimeout() should throw TimeoutCancellationException if timeMillis<= 0

[baltiyskiy]

Documentation for withTimeout states that it throws a TimeoutCancellationException if the timeout was exceeded. However, the implementation throws a CancellationException if timeMillis <= 0. First, it looks like the implementation directly violates the documentation, because that's a case of an already exceeded timeout. Second, there's no notice of CancellationException in the docs altogether. Third, it makes no sense to state that the method throws a DerivedException when it throws BaseException, because one has to catch BaseException instead.