Adding cpp implementation

[Peter9192]

It would interesting to explore having an alternative implementation of CLASS e.g. in c++ or rust. That would pave the way for swapping the code with some other (more compute-heavy) models as well.

Some starting points

• MDN docs on compling c/c++ to wasm
• this series of blog posts
• this starter package
• the cpp BMI interface
• the example cpp BMI implementation