Documentation updates for 4.16. New stuff includes refcount_t

documentation, errseq documentation, kernel-doc support for nested
structure definitions, the removal of lots of crufty kernel-doc support for
unused formats, SPDX tag documentation, the beginnings of a manual for
subsystem maintainers, and lots of fixes and updates.

As usual, some of the changesets reach outside of Documentation/ to effect
kerneldoc comment fixes.  It also adds the new LICENSES directory, of which
Thomas promises I do not need to be the maintainer.
-----BEGIN PGP SIGNATURE-----
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=Z15Z
-----END PGP SIGNATURE-----