When setting sun and moon to visible = false, dynamic shadows would not display any more.
In combination with the high-resolution skyboxes, they increase graphical quality quite a bit.
Setting sun and moon to an empty texture instead keeps dynamic shadows intact.
When using the skybox.add function, worlds fail to load with the following error:
/skybox/init.lua:90: attempt to call field 'add' (a nil value)
Using table.insert instead allows this to work without any added dependencies.
