bibdocfile: fix documentation WRT --with-version
bibdocfile: fix documentation WRT --with-version

* --hard-delete CLI option was not handling correctly
  the --with-version option, in particular when
  multiple versions were specified or when 'all' is
  specified. Now only one version is explicitly
  accepted and the documentation has been improved.

tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio