Multiplenames

Changed dunder-getattr to return a list if more than one value. The 'name' property now looks at whether the name is singular or a list. If it's a list, iterates through them to find the preferred name. Also added an 'aka' property to return the list of other names. Could perhaps refactor the Element to tuple handling into a separate utility function.
I'm not certain if the change to dunder-getattr will break other tags in a more complex example (not sure what other tags can be repeated in this way).
Cheers,
Chris.