Proposal: add properties that represent TNU relationships about tnc

[mdoering]

It opens up the standard for alternative representations. This shifts the problem to consumers that now have to check different places for the same information. I personally think this is a bigger problem than for the producer, so I would try to avoid this as much as possible. It is also an issue you find in DwC, ABCD and TCS1 where there are parsed and unparsed strings for the same thing. The more options a standard has, the less of a standard it is :)

[camwebb]

@mdoering Good point. I concede that for standardization of data transfer, having a single way to 'officially' do something is best.