说明：  非常好用的三次样条插值算法，把网上流传的算法，改造成一个方便使用的C++类，使用时可以从此类继承一个类，封装成你自己的类型
(Very easy to use cubic spline interpolation algorithm, the algorithm circulated on the Internet, transformed into an easy to use C++ class, when using a class can inherit from this class, package into your own type)