Update to Godot 4.x

[LinuxUserGD]

Fixes #11
Toggle-comment is broken and not sure if the input map is correct, otherwise should work fine.

[Calinou]

Thanks for carrying out this work!

I'll need to see how I can provide both options on separate URLs, with each minor version being in its own folder. To preserve compatibility with existing URLs out there, the top-level gdscript-online.github.io should redirect to the latest 3.x version available. This should likely be done using a symbolic link, so that we don't use an HTML redirect that would remove parameters from the URL.