handle case where len(coords) == 1 (for all coords) with empty tuples
First version that works already somewhat with Cycle 2 IFS output (ICMGG files tested). It creates an index, e.g.
gribscan-index -n 48 ICMGG*
and builds a dataset atm2d.json file via
gribscan-build -o <directory> --prefix /work/bm1235/a270046/cycle2-sync/tco3999-ng5/01_20Jan-25Jan2020_tco3999_fesom/ ICMGG*index
Some more fine tuning needed to include all time steps for some variables (e.g. 2t) and possibly renaming (e.g. "cells")