Modernising the code, improving images

src/Cxx/IO/3DSImporter.cxx

src/Cxx/IO/3DSImporter.md

src/Cxx/IO/CMakeLists.txt

src/Cxx/IO/ConvertFile.cxx

src/Cxx/IO/ConvertFile.md

src/Cxx/IO/DEMReader.cxx

src/Cxx/IO/DumpXMLFile.cxx

src/Cxx/IO/DumpXMLFile.md

src/Cxx/IO/ExportPolyDataScene.cxx

src/Cxx/IO/ExportPolyDataScene.md

src/Cxx/IO/FindAllArrayNames.cxx

src/Cxx/IO/FindAllArrayNames.md

src/Cxx/IO/GLTFExporter.cxx

src/Cxx/IO/GLTFImporter.cxx

src/Cxx/IO/GenericDataObjectReader.cxx

src/Cxx/IO/ImageReader2Factory.cxx

src/Cxx/IO/ImageWriter.cxx

src/Cxx/IO/ImageWriter.md

src/Cxx/IO/ImportPolyDataScene.cxx

src/Cxx/IO/ImportToExport.cxx