We want to always group the three shapefiles, that is actually nine

files, that make up a snapshot into a directory that contains only
these files. We hope that this will ease the handling of
snapshots. For now, this is useful in program
test_successive_overlap. So, in program extraction_eddies, create the
shapefiles in a directory called Snapshot. As we cannot create the
directory from Fortran (in Fortran 2003, it becomes possible in
Fortran 2008), we have to wrap the Fortran executable in a shell
script "extraction_eddies.sh". In the same way, read from a directory
Snapshot_old in programs test_read_eddy and test_read_snapshot and
create scripts "test_read_eddy.sh" and "test_read_snapshot.sh".

Reference the shell scripts "extraction_eddies.sh",
"test_read_eddy.sh" and "test_read_snapshot.sh" in JSON test files.

In program test_successive_overlap, finally read two snapshots, from
directories Snapshot_1 and Snapshot_2. Pass to successive_overlap the
date of the second snapshot. Use new variables corner_deg and step_deg
to avoid converting to rad twice.

Create directory Snapshot in Tests/Input/Region_4/2006_01_01.