def delete(unique_id)
      rsp = post("<delete><id>#{unique_id}</id></delete>")
      success?(rsp.body) or log_error(rsp.body)
    end
def delete(unique_id)
      rsp = post("<delete><id>#{unique_id}</id></delete>")
      success?(rsp.body) or log_error(rsp.body)
    end
deletes <tt>unique_id</tt> from the index