OpenCV 3 compatible demo

[rajatvikramsingh]

Modified the demo file for opencv3 compatibility.

[kornerc]

Thank you for your contributions!

Are you able to run the demo with your changes? When I run the demo I get an error:

OpenCV Error: The function/feature is not implemented () in detectAndCompute, file ~/opencv-3.2.0/modules/features2d/src/feature2d.cpp, line 154
terminate called after throwing an instance of 'cv::Exception'
what(): ~/opencv-3.2.0/modules/features2d/src/feature2d.cpp:154: error: (-213) in function detectAndCompute