Calling the constructor alone is not enough if the class to be
instantiated is not a base class.
This commit adds two functions, one for retrieving the the extension
class reference, the other to construct an instance using the
constructor and the extension class reference.
- Add MethodBind call (besides ptrcall), since vararg methods don't work
with ptrcall.
- Fix argument name in register constant function to the way it
actually is used in the engine.
- Change the integer constant type to GDNativeInt to keep it consistent.
- 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
