Convert a std::function to a function pointer and context pointer, for use with C API callbacks.

Callable.hpp

    /**
     * Usage:
     * ```
     * std::function<void(int32)> callback; // This should be stored as e.g. class member
     * ...
     * addInt32Callback (wrapCallable<int32>(callback), &callback);
     * ```
     * @tparam T
     * @tparam Callable
     * @return function pointer
     */
    template<typename... T, typename Callable>
    auto wrapCallable(Callable const&) -> void (*)(T..., void*)
    {
        return +[](T... data, void* context)
        {
            (*static_cast<Callable*>(context))(data...);
        };
    }