I recreated the intent of `rdm.h` into a new, more C++-oriented, `rdmconst.h` file. Notes about the file:
- Uses `constexpr` instead of `#define`s.
- Fixes some spelling mistakes from the standard by introducing new constants, but keeping the old constants and tagging them with `[[deprecated("spelling")]]`.
- Puts everything into an `rdm` namespace.
Feel free to make comments and suggestions. Consider this a beta version.
The file is attached.