Add gmp and mpfr patterns for embedded-library tag

The latest MetaPost depends on these two libraries, so
texlive-binaries could accidentally end up with them embedded.
Correct the description for debug-symbols-directly-in-usr-lib-debug
Improve two examples in infofiles.desc

Hardly any manuals are still using "@dircategory Development"; they
mostly seem to be in "@dircategory Software development".

Also, it's unlikely that an info file lacking a @direntry will have
@dircategory, so we might as well include a @dircategory in that
example too, which will avoid any doubt as to how to arrange them.
t/tests/README: Update some paths

[nthykier: Fix a typo in the corrected path]

Signed-off-by: Niels Thykier <niels@thykier.net>
d/changelog: Add changelog entries for Samuel's patches

Signed-off-by: Niels Thykier <niels@thykier.net>