Return value
     array - a two dimensional, nested array
     indicated by the name of the newsgroup, every entry contains
     information about the newsgroup:
     
        $groups[newsgroup_name]['group']
        Name of the newsgroup
       
        $groups[newsgroup_name]['last']
        Number of the last article
       
        $groups[newsgroup_name]['first']
        Number of the first article
       
        $groups[newsgroup_name]['posting']
        values: y - yes, 
        n - no,
        m - moderated)