2.7.5. *.nml input files

input.nml is a template input file, which serves a dual purpose:

1. Define a simple test case, that should not take more than about a minute to run on an average laptop
2. Act as a template file, to be copied to input files whatever.nml whose names also define the location of output files, which appear in data/whatever/ directories. Here whatever may be chosen arbitrarily, and could for example be run1, run2, or 2019-08-22a, or L=30px_levels=6-9.