[m-rev.] for review: Add string.is_well_formed predicate.

[Julien Fischer]

On Thu, 12 Sep 2019, Peter Wang wrote:

> library/string.m:
>    Add predicate to test if a string is in UTF-8 or UTF-16,
>    depending on the target language.
>
> NEWS:
>    Announce the addition.
>
> tests/hard_coded/string_well_formed.exp:
> tests/hard_coded/string_well_formed.m:
>    Add basic test case.
>
> tests/hard_coded/string_well_formed_utf8.exp:
> tests/hard_coded/string_well_formed_utf8.exp2:
> tests/hard_coded/string_well_formed_utf8.exp3:
> tests/hard_coded/string_well_formed_utf8.inp:
> tests/hard_coded/string_well_formed_utf8.m:
>    Add more thorough test for UTF-8. The input file is from
>    https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-test.txt
>
> tests/hard_coded/Mmakefile:
>    Enable the tests.

That's fine.

Julien.