add map for unused files
add map for unused files

unused.ditamap contains references to all topics currently available in
the project that are not used in any maps.  I created it to help me
review the unused topics. They are not in  any particular order in the
map.

dita4publishers/org.dita4publishers.html5,dita4publishers/org.dita4publishers.html5,dita4publishers/org.dita4publishers.html5,dita4publishers/org.dita4publishers.html5,dita4publishers/org.dita4publishers.html5