[m-rev.] for review: Add closeable channels to the standard library.

[Julien Fischer]

Hi Peter,

On Mon, 17 Feb 2020, Peter Wang wrote:

> library/thread.closeable_channel.m
>    Add the new module. It omits two operations from thread.channel.m:
>    - untake, because it is deprecated
>    - duplicate, because I'm not sure what it's useful for in practice
>
> library/MODULES_DOC:
> library/library.m
> library/thread.m:
> NEWS:
>    Mention the new module.

That's fine; can you please also extend the test suite with a test
that exercises the basic functionality of the new module.

Julien.