Add man pages; update via make from html branch

Add a manpage section to the documentation, and arrange for man/*.html
and man.html to be automatically updated via "make".  Leave the commit
after any update to the user.

Thanks to Gabriel Filion for discussions that helped simplify an
earlier approach.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>
Add a related projects section

Signed-off-by: Rob Browning <rlb@defaultvalue.org>