Section 58. The by-laws may prescribe what shall constitute proper notice of meetings of the directors. A notice or waiver of notice need not specify the purpose of any special meeting of the directors unless required by the by-laws. Notice of a meeting need not be given to any director, if a written waiver of notice, executed by him before or after the meeting, is filed with the records of the meeting, or to any director who attends the meeting without protesting prior thereto or at its commencement the lack of notice to him.