Update asciidoc_setXhtmlRendition function.
    
    - Previously, we were indenting markup of final html files using tidy
      program. Tuning up tasks shouldn't be written inside the render
      module. This update changes asciidoc_setXhtmlRendition function to
      call the tuneup parent module which takes care of tuning up html
      files. Tuneup module uses the xmllint program instead of tidy.
    
    - Previously, the prepare module was considering the tidy package as
      required. This update changes the packages function to remove tidy
      from list of required packages. xmllint program is part of libxml2
      package which is already in the list of required packages.