Document the @dir and @ empty keyword
Deprecate @dirrm and @dirrmtry
Keywords now use ucl files

Differential Revision:	https://reviews.freebsd.org/D807
Reviewed by:	wblock, bjk
Sponsored by:	Absolight


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45656 c2e8774f-c49f-e111-b436-862b2bbc8956
And make a title actual english.

Sponsored by:	Absolight


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45657 c2e8774f-c49f-e111-b436-862b2bbc8956