Symbolic links in the Aviso `All_SymbolicLinks` directory point to
absolute paths so they do not work (I think) if we choose to mount the
Aviso directory through sshfs.

We want to add the possibility to choose a date in the slice. Note
that the script was created when there was only a single date in the
collection of shapefiles, and the script did not really change since
then.

Preparing to add an optional argument.

Preparing the option to save the figures.

Rename dummy arguments `hshpc_(cyclo|anti)` to `h_(cyclo|anti)`. They
are not SHPC handlers, they are oriented slice handlers.

It is not an SHPC handler, it is an oriented slice handler.

Rename function `process_1_file` to `process_1_date`.

In method `__init__` of class `SHPC_class`. As a consequence, we
remove the dummy argument `def_orient` of `__init__`.

Read date from `date_range.txt` in program `inst_eddies` and update
date in `date_range.txt`at the end of execution of program
`inst_eddies`, remove date from the namelist `main_nml`.

Preparing to use a second unit.

Move file `shpc_create.f90` to directory `Common/Tests`. `shpc_create`
is no longer used in program `inst_eddies` since commit dc51b1bd.

Rename procedure `get_slice_dir` to `get_ori_slice_dir`.

Rename type `shpc_slice_handler` to `ori_slice_handler`.

This is a change in the format of an SHPC. I have realized that the
program `inst_eddies` may not find any eddy at a given date and
orientation (as in the test `No_eddy`), so we cannot guarantee that
the first date present in the shapefiles corresponds to the first line
in `ishape_lat.txt`. So we store the initial date explicitly in a text
file. We could deduce the final date from the initial date and the
number of lines in `ishape_lat.txt` but we can avoid counting the
lines and just store the date range.

Else the output of `subprocess.run` comes before the print statements
in the script.

Clarifying the logic: the Fortran program only appends to an already
created SHPC slice.

Use `create_slice.py` in tests of program `inst_eddies`. The namelists
then have to be written to a file, to be read both by
`create_slice.py` and by the program `inst_eddies`.

The program `test_mean_speed` no longer needs the SHPC directory since
commit 8eadc458.