Glyph: Treatment of empty values vs. None

[madig]

While (de)serializing a glif file's <outline> element, it is written if aGlyph.outline is Some(...) and not if it is None. The official(?) https://github.com/unified-font-object/ufoNormalizer/ will omit the element during "serialization" if it is empty. I think norad should do the same, but doing so makes the tests fail because no outline element is considered None and an empty one is Some(Outline { components: [], contours: [] }).

One way to handle this is to not de/serialize values if they are empty, assigning None instead if Some(empty_something).

Another option would be to treat some values with None and empty values as the same. This would need more thought because for some values, you need to distinguish between "no value set" and "empty value".

Yet another would be to not use Option in Glyph and test for emptiness when serializing.

[madig]

I removed a lot of Options and we skip empty contours and the like. This is now moot I think.