List property types should export element type specifications

[ChALkeR]

See #34 — for property list<Item> items, we now export ["qmlpropdef", "items", "list"] and omit the element type information.

That is better than not parsing them at all, but we should export the additional type information in some form, hopefully — without breaking backwards compatibility.

/cc @akreuzkamp, any opinion on how this should be presented in the current output format?

Long-term, I would prefer to migrate from arrays to objects for such things (think ESTree).