Adding an example to integration of DXCam and OpenCV for real-time screen capture and FPS display

[lshw54]

This example demonstrates the usage of DXcam for capturing the screen and OpenCV for displaying the capture and the frames per second (FPS) on the captured screen.

[atsimourtos]

Do you think it's possible to specify a specific window process instead of region? I think currently there is option for dxcam to limit the capturing on a specific window instead the whole screen.

EDIT: Found related conv here https://github.com/ra1nty/DXcam/issues/30