name: Optionally, a single parameter name (say "as.fun").
allow.unknown: Allow access to configuration of variables that are not pre-defined in NMdata. This should only be needed in cases where say another package wants to use the NMdata configuration system for variables unknown to NMdata.
Returns
If name is provided, a list representing one argument, otherwise a list with an element for each argument that can be customized using NMdataConf.