Allow empty return statements

[eschnett]

No description provided.

[eschnett]

Closes #443.

[pxl-th]

Does it allow multiple return statements?

function ker()
    ...
    if something()
       return
    end
    ...
    if something_else()
       return
    end
    ...
    return
end

[eschnett]

It does. But – should it?

[pxl-th]

I'd like to have this option. Right now I find myself writing wrapper functions that I call from the kernel just to be able to use return statements.

[eschnett]

ping Could you let the CI workflows run for this PR?