[Nml-wg] Reference subsection

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