CDate

代码说明：

  主要编写的是一个是期类，包括日期的加法，减法，大于符号，小于符号的重载，和一些常用符号的重载，及日期类的一些常见运算(Is mainly written in a period of class, including the date of addition, subtraction, greater than symbol, less than symbols overloaded, and some common signs of overload, and the date of the class some common operations)