It now supports varargs directly, so the argptr magic is no longer needed.

All those hardcoded max number of arguments from 3.x days could be changed
to properly use varargs, and further cleanup the code. Volunteers welcome :)

It will now contain `bin/` as topmost folder, and both release and debug
artifacts are uploaded (separately for now).

Would be nice to change the release process eventually to include all
platforms and targets in a single zip.

Uses an absolute path for compatibility with 4.1.x.

We can switch to relative paths for both the icon and the libraries once
we start targeting 4.2 as minimal version.

Add class reference support with godot-cpp#1374.