[WIP] Header only

[kerautret]

PR Description

Making header only lib, useful to construct standalone tools
Work in progress:

• DGtal.dir/src/DGtal/base/Bits.cpp
• DGtal.dir/src/DGtal/base/Common.cpp
• DGtal.dir/src/DGtal/io/Color.cpp
• DGtal.dir/src/DGtal/io/boards/Board2D.cpp
• DGtal.dir/src/DGtal/io/boards/Board3D.cpp
• DGtal.dir/src/Board/Board.cpp
• DGtal.dir/src/Board/Path.cpp
• DGtal.dir/src/Board/Rect.cpp
• DGtal.dir/src/Board/ShapeList.cpp
• DGtal.dir/src/Board/Shapes.cpp
• DGtal.dir/src/Board/Transforms.cpp

Checklist

• Unit-test of your feature with Catch.
• Doxygen documentation of the code completed (classes, methods, types, members...)
• Documentation module page added or updated.
• New entry in the ChangeLog.md added.
• No warning raised in Debug mode.
• All continuous integration tests pass (Github Actions & appveyor)