Redirecting headers for format and ranges

code/include/cxx20format

+#include <version>
+#ifdef __cpp_lib_format
+  #include<format>
+  namespace fmt = std;
+  using std::format;
+#elif __has_include (<fmt/format.h>)
+  #define FMT_HEADER_ONLY
+  #include<fmt/core.h>
+  #include<fmt/format.h>
+  using fmt::format;
+  #warning Using external format.h header from the fmt library.
+#endif
+

code/include/cxx20ranges

+#include <version>
+#ifdef __cpp_lib_ranges
+  #include<ranges>
+  namespace sr = std::ranges;
+  namespace sv = std::views;
+#elif __has_include (<range/v3/all.hpp>)
+  #include<range/v3/all.hpp>
+  namespace sr = ranges;
+  namespace sv = ranges::views;
+  #warning Using rangesv3 3rd party library
+#else
+#error No suitable header for C++20 ranges was found!
+#endif
+