Function format

--- This a C++ universal sprintf in the future. ** @pitfall: The behavior of vsnprintf between VS2013 and VS2015/2017 is different ** VS2013 or Unix-Like System will return -1 when buffer not enough, but VS2015/2017 will return the actural needed length for buffer at this station ** The _vsnprintf behavior is compatible API which always return -1 when buffer isn't enough at VS2013/2015/