def from_dir(dirname)
      unless File.directory?(dirname)
        raise "'#{dirname}' is not a directory or doesn't exists"
      end
      @dirname = File.expand_path dirname
      @ctime = DateTime.now
      _load_from_dir
      self
    end
def from_dir(dirname)
      unless File.directory?(dirname)
        raise "'#{dirname}' is not a directory or doesn't exists"
      end
      @dirname = File.expand_path dirname
      @ctime = DateTime.now
      _load_from_dir
      self
    end
Build a catalog from a directory