[m-rev.] for review: convert NEWS file to markdown and begin restructuring it

[Peter Wang]

On Mon, 30 Dec 2019 23:56:51 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
> +* We have changed the semantics of `int.abs`/1 so that it throws an exception
> +  if its argument is equal to `int.min_int`. The old behaviour of this function
> +  is provided by the new function `int.unchecked_abs`/1.

Another minor thing. I think symbol/arity notation looks better when
written like

    `int.abs/1`

instead of

    `int.abs`/1

both when reading as plain text and in the rendered HTML.

Peter