Philippe 12/12/2022: aircrafts: restructure to compute next position (instead of computing current position)
This is necessary to allow transfer of all aircraft data between processes (to be developed)

Philippe 09/12/2022: flyers: correction for 'FIX' aircrafts if store timestep smaller than model 1 timestep

Philippe 02/12/2022: aircraft_balloon_evol: first cleaning + better organisation of the source + correction of several bugs

Philippe 25/11/2022: flyer data in files: add NMODELHIST + compute/write LWC only when it makes sense

First version: some cleaning, deduplication and optimisation not yet done

Philippe 25/11/2022: rewrite STATPROF_INSTANT algorithm (does not depends on model timestep anymore => independent of model)

Philippe 16/11/2022: profilers: rename VISI -> VISIGUL + compute visibilities only when it has a meaning (there were NaN if not...)

Philippe 27/10/2022: datetime: add <= and > operators and improve older comparison subroutines (more robust but slower)

Philippe 21/10/2022: bugfix: ground_param_n: communicate halo values between processes for OUT variables

+ more efficient use of grid variables