Update 18-appendix.md

[zmilan]

Since 'topic' is made dynamic and there is no track of it, off will never delete anything. So fast solution is to send event name (that can contain separation 'like module.part.event') and than delete all topics for it.

[addyosmani]

Thanks! In your PR, you use a custom namespace (Fuisz?) which I think may have been your own as we don't use it in the appendix. I have however landed a change using the Cranium namespace and referred back to this issue so folks know you contributed it. Cheers!