Update manual functionality:
    
        - Add manual_removeCrossReferences.sh -- This function removes a
          documentation entry cross refereces from all texinfo files the
          documentation manual is built on.
    
        - Add manual_restoreCrossReferences.sh -- This function restores
          old missing cross references back into their link form. This
          function applies in those cases where new documentation entries
          are added to documentation structure. It is a verification
          looking for matching documentation entries previously defined as
          missing. This function relays in the missing message output
          produced by functions like manual_removeCrossReferences, in
          order to return them back into the link format.
    
        - Update manual_createEntry.sh to use
          manual_recoverCrossReferences.
    
        - Update manual_removeEntry.sh to use
          manual_removeCrossReferences.