[WISH] default values

[TeunHuijben]

Would it be possible to use the default attribute values when adding a node or edge? So, when we add a node without providing all feature values, the values that are not provided are filled with the default values? Otherwise, what does the default value actually do, apart from determining the dtype/shape of each attribute?

Apart from probably a difficult implementation, are there reasons why we want to force users to provide ALL feature values when adding a node or edge?

This is not urgent, just wanted to make an issue to discuss this

[JoOkuma]

It's a great suggestion, I'm working on refactoring the add_node|edge_attr_key and this will be taken into consideration.
Related to #193