Auto-generate MPI API bindings from MPI standard

The MPI Forum (which distributes the MPI standard) provides a [machine-readable version of the MPI API](pympistandard/src/pympistandard/data/apis.json). (This repository also includes some Python code that we are free to ignore.)

I have used this to generate MPI bindings for C and Fortran for other projects. [Here](https://gist.github.com/eschnett/0b4fea9ab6aaf56044ff8b0e4596888c) are autogenerated Julia wrappers for MPI 5.0.

I'd be happy to turn this into a PR (including the actual code generator, of course!) if there is interest.

The API comes even with documentation for each function argument!