def to_pretty
      to_a.each_with_index.map { |e,i| "%5d  %s" % [i+1, e.shelljoin] }.join("\n")
    end
def to_pretty
      to_a.each_with_index.map { |e,i| "%5d  %s" % [i+1, e.shelljoin] }.join("\n")
    end
Return entries just like running `history` in your shell.
 @return [String] pretty representation of the entries