alternatecalendar: support solar terms in Chinese lunar calendar
In Chinese lunar calendar, solar terms, also known as "节气", are points in time that mark the changing seasons and the solar movements. There are 24 solar terms in total, with each term representing a specific astronomical event or natural phenomenon. These solar terms are based on the position of the sun relative to the Earth and are used to determine the timing of various agricultural activities, traditional festivals, and other cultural practices in China.
This allows the calendar to show solar terms under day numbers, and the full alternate date under the Gregorian date will contain a solar term of the day if the current day matches a solar term.
Closes #11 (closed)
Edited by Fushan Wen