All non-ASCII files should be encoded in UTF-8. So far, the ZSH script
`Scripts/developer_scripts/detect_wrong_encoding` detects wrong encoding
in source/header files of include/, src/, and doc/.
When CORE_arithmetic_kernel and LEDA_arithmetic_kernel are used, then
one should have:
#include <CGAL/CORE_arithmetic_kernel.h>
#include <CGAL/LEDA_arithmetic_kernel.h>