- Fix library loading and initialization.
- Add extra methods/parameters in the interface needed by extenstions.
- Add Variant destructors and functions for extracting values and
creating Variants from values.
* The harcoded 8 slots are no more and impose limits in the new extension system.
* New system is limitless, although it will impose small performance hit with a mutex.
* Use a token to request the instance binding.
**Warning**: Mono will most likely break as a result of this, will need to be modified to use the new system.
* Deprecates GDNative in favor of a simpler, lower level interface.
* New extension system allows registering core engine classes.
* Simple header interface in gdnative_interace.h
