Modernising the code, improving images

src/Cxx.md

src/Cxx/RectilinearGrid/RGrid.cxx

src/Cxx/RectilinearGrid/RGrid.md

src/Cxx/RectilinearGrid/RectilinearGrid.cxx

src/Cxx/RectilinearGrid/RectilinearGrid.md

src/Cxx/RectilinearGrid/RectilinearGridToTetrahedra.cxx

src/Cxx/RectilinearGrid/RectilinearGridToTetrahedra.md

src/Cxx/RectilinearGrid/VisualizeRectilinearGrid.cxx

src/Cxx/RectilinearGrid/VisualizeRectilinearGrid.md

src/CxxHowTo.md

src/Python.md

src/Python/RectilinearGrid/RGrid.md

src/Python/RectilinearGrid/RGrid.py

src/Python/RectilinearGrid/RectilinearGrid.py

src/Python/RectilinearGrid/VisualizeRectilinearGrid.py

src/PythonHowTo.md

src/Testing/Baseline/Cxx/RectilinearGrid/TestRGrid.png

...ting/Baseline/Cxx/RectilinearGrid/TestRectilinearGrid.png

...line/Cxx/RectilinearGrid/TestVisualizeRectilinearGrid.png

src/Testing/Baseline/Python/RectilinearGrid/TestRGrid.png