Modernising the code

src/Cxx/ImageProcessing/Pad.cxx

src/Cxx/Images/Actor2D.cxx

src/Cxx/Images/BackgroundImage.cxx

src/Cxx/Images/BackgroundImage.md

src/Cxx/Images/BorderPixelSize.cxx

src/Cxx/Images/CannyEdgeDetector.cxx

src/Cxx/Images/Cast.cxx

src/Cxx/Images/Cast.md

src/Cxx/Images/CenterAnImage.cxx

src/Cxx/Images/CenterAnImage.md

src/Cxx/Images/Colored2DImageFusion.cxx

src/Cxx/Images/Colored2DImageFusion.md

src/Cxx/Images/CombineImages.cxx

src/Cxx/Images/CombineImages.md

src/Cxx/Images/CombiningRGBChannels.cxx

src/Python/Images/Actor2D.py

src/Python/Images/BackgroundImage.md

src/Python/Images/BackgroundImage.py

src/Python/Images/Cast.md

src/Python/Images/Cast.py