Make the existing -d (depth) option apply to the -H (static HTML

Make the existing -d (depth) option apply to the -H (static HTML
report) mode, transforming its output from a single HTML file giving
a report for one directory with no crosslinks to a collection of
HTML files with crosslinks between them.

I've also added a special 'max' value to -d (meaning no depth
limit), which also works when used in text mode; I've added -o to
specify an output file for both text and HTML report modes; and I've
also documented -d, which I had previously forgotten to do (but
nobody seems to have noticed :-).

git-svn-id: svn://svn.tartarus.org/sgt/agedu@8880 cda61777-01e9-0310-a592-d414129be87e