Speed up taxon-group pairs querying
At the moment the C-level get.inpind.parval.taxon.group.pairs.reach.habitat
query for parameter values takes ca. 50% of streambugs.get.sys.def
runtime.
It queries for all possible pairs so in principle it could be sped up by querying only food-web stoichiometrically related pairs, as it used to be before re-factoring from R for-loop to C vectorised functions querying.