Pass pointer between python and C++

[sturkmen]

@Kelvin

CV_EXPORTS_W bool imencode( const String& ext, InputArray img,
                            CV_OUT std::vector<uchar>& buf,
                            const std::vector<int>& params = std::vector<int>(),
                             std::vector<unsigned char*>& workspace);

try

CV_EXPORTS_W bool imencode( const String& ext, InputArray img,
CV_OUT std::vector& buf,
const std::vector& params = std::vector(),
InputArray workspace);