GDScript support
I've started experimenting with adding [GDScript](https://docs.godotengine.org/en/latest/tutorials/scripting/gdscript/gdscript_basics.html) support, the scripting language used by the [Godot Engine](https://godotengine.org/).

Specifically, the GDScript implementation in the 4.0 version of the engine, since that has had many performance improvements over the 3.x branch, making it useable for doing more then basic game scripting.
And before someone mentions it, I'm aware there is C# support for Godot and Kaitai, but GDScript is the default and very popular with Godot users.

I've done a basic proof-of-concept implementation in the compiler, and a minimal struct implementation. I'll need to clean it up before posting a pull request, but I'm hoping to do that soon.

Just posting this issue to raise awareness that this is being worked on.