Addition of htdbm documentation. nroff was meant to be generated,

but wasn't.  I suspect deps.xml in build/ needs to be modified, but
could someone else with more of a clue assist here, thanks.

Submitted by: Matt Brubeck <mbrubeck@cs.hmc.edu>
Reviewed by:  Jason Lingohr <jsl@apache.org>



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@159095 13f79535-47bb-0310-9956-ffa450edef68