Exercises

1. In the Destinations class, we only used one upvalue. Add another upvalue and play around with it. Which upvalue is at which pseudo-index?
2. Try to modify the second upvalue in a function and see if the value is persisted the next time the function is called. How about when it is accessed in another function?
3. In LuaType.hpp, add LuaType::lightuserdata and implement a structure for it, named LuaLightUserData. Support this case in the executor and helper functions. You do not need to support this type when popping values from the Lua stack.