Enable the use of __index and __newindex metamethods

[JuneCarya]

Adds the ability to use __index and __newindex metamethods in classes.
Infinite recursion is avoided by first changing the original table keys __index and __newindex of the class to __get and __set, and using a proxy table that accesses the renamed metamethods on the actual class instance.
Instantiating a class now always returns a proxy object instead of the actual class instance.