Method getIndex

src/main/java/com/nlf/calendar/SolarSeason.java:120–122

获取当月是第几季度 @return 季度序号，从1开始

()

   * @return 季度序号，从1开始
   */
  public int getIndex() {
    return (int) Math.ceil(month * 1D / MONTH_COUNT);
  }

  /**
   * 季度推移