api-doc: return status for notmuch_query_search_threads_st ...

[David Bremner]

Gaute Hope <eg at gaute.vetsj.com> writes:

> Hi,
>
> I am switching from the deprecated notmuch_query_search_threads to
> notmuch_query_search_threads_st, but the api-documentation does not
> specify what status values are returned and what they mean.
>
> The same goes for notmuch_query_search_messages_st (...).
>

They both can return OUT_OF_MEMORY, XAPIAN_EXCEPTION, and SUCCESS.
It would be great if someone (TM) would work up, and test the output of
doxygen on, a patch to lib/notmuch.h.

d