Currently, the Span object's parent can be both a Span, or a SpanContext object.

This is resulting in multiple parts of the code where one has to handle the Span parent case, and the SpanContext parent case.

It would be great if we decided to go one or the other. As a proposal, I'll suggest it should be a Span, as currently Span, as it contains additional data in addition to the context such as Events.