[Nml-wg] Reference subsection

[Freek Dijkstra]

Hi all, and Jeroen and Roman in particular,

I just pushed some changes to the subsection describing References,
adding small diagram showing all cardinalities, and making a distinction
between allowed and defined relations.

Please check if there are no errors or omissions.

Next up: I think most relations needs a slightly better descriptive
text. Right now most relations just say there may be a relation between
two objects, but don't tell what that relation means.

Jeroen, commit 21dcef59 also closes the open artifact on inverse
multiplexing adaptation functions. I think the existing text was already
good, but I moved it from a footnote in De-Adaptation to the Adaptation
description.

Regards,
Freek