#list doesn't behave as it should?

Forgot to thank you for this gem ;)

Mac.addr returns a string. "mac", and the singlemethod #list is not applied to it.
So I need:  Mac.addr.respond_to?(:list) . Can't get any uglier.

Also, a better approach here: https://github.com/tsilen/macaddr
The singleton method #list really doesn't make sense.
