Adding Numba

For those looking to optimize some Python code in a-Shell or Carnets, Numba may be a reasonable option and worth inclusion (and a potential alternative to things like Cython, which are harder to add due to the limitations with WebAssembly)

As [Numba's architecture]( https://numba.readthedocs.io/en/stable/developer/architecture.html ) is designed to generate LLVM IR, which LLVM in turn compiles for the target architecture's assembly code, this may be more amenable to generating optimized codes for WebAssembly

This may still require more work upstream. That said, it seems like upstream is interested in this work

* https://github.com/numba/llvmlite/issues/836
* https://github.com/numba/numba/issues/3284