Investigate how to best get rid of slice pointers

[nscuro]

Currently, we're using slice pointers (e.g. *[]string) to work around a limitation of encoding/xml.

It works, but it's not pretty. This is painfully obvious when trying to iterate over elements of those slices and having to dereference and nil check all the time. It'd be great if we could just have normal slices instead.

Most likely, we'll have to introduce a lot more custom (de-)serialization code specific to the XML format to make this work.