base64 编解码实现，其中有两种方式，一种是比较普通的c++ stl实现,另一种是根据国外的某人用java写的程序 用c++的方式重新实现的-base64 codec implementation, where there are two methods for a more general c++ stl implementation, and the other is based on a person abroad programs written using java with c++ way of re-implementation