Fix noexcept and constness

Could probably add more const-correctness to jl::value`

Initial Prerelease

The API is fully usable including variable, struct an array manipulation, calling functions with parameters and getting results. Non-const references and pointers to Julia values can be requested and used to communicate between the languages.

Known bugs

• Arrays may not be alive if they are not used the very next jl:: call. This has to do with the garbage collector working too early.