This section describes how months are counted in Chinese calendar.
In Chinese calendar, months are lunar months. This means the first day of each month beginning at midnight is
the day of the astronomical new moon.
Because new Moon happens every 29.53 days, the number of days in a month is changing between 29 days and 30 days.
In order to synchronize with the tropical year, an extra month, leap month, will be inserted. The exact rule of
how the leap month should be inserted is very complex. You can read more details on my other book
"Herong's Notes on Chinese Calendar"
