STATEFUL FUNCTIONS!
Any stateful function now works and is properly cleaned up, thanks to some additional metatables that are associated with the function values.
This lays the ground work for class bindings, but that's a far off dream. For now, table retrieval and `operator[]` is what's for dinner.
Member functions now work as well for set_function. If performance of `new`ing a type ever becomes too large, we can create a custom allocator for the std::shared_ptr's of the types. We can also up-front allocate for the unordered_map as well.
It'll be up to @Rapptz's to make further changes to make sure GCC compiles, but the core of the functionality is there and my work is essentially done.
Class bindings are up next, but really I don't want to even touch those. :c