* Allows calling into native extensions directly with a pointer
* Makes it easier to implement some APIs more efficiently
* Appears with a "*" in the documentation for the argument.
* Implementing the pointer handling is entirely up to the implementation, although the extension API provides some hint.
* AudioStream has been implemented as an example, allowing to create NativeExtension based AudioStreams.
* New syntax is type safe.
* New syntax allows for type safe virtuals in native extensions.
* New syntax permits extremely fast calling.
Note: Everything was replaced where possible except for `_gui_input` `_input` and `_unhandled_input`.
These will require API rework on a separate PR as they work different than the rest of the functions.
Added a new method flag METHOD_FLAG_OBJECT_CORE, used internally. Allows to not dump the core virtuals like `_notification` to the json API, since each language will implement those as it is best fits.
* 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
