Feature Request: Adding Cupy Support

Hi,

I was looking for a python opencv alternative to `cv2.imencode('.jpeg', cv2.imread(image_path, cv2.IMREAD_GRAYSCALE))` and found this library.

A way to save computation time would be using cupy arrays, so a copy from CPU to GPU and vice versa could be avoided.

Cupy is a numpy-like python package, but it's using the NVIDIA GPU instead of the CPU.