Return None from `open_shpc` when `ishape_last.txt` is not found,
instead of `[len(readers["extremum"]) - 1]`, as needed by
`plot_eddy_contours.py`. So that we can take another action in another
script.

Move functions `in_window` and `open_shpt` from
`plot_eddy_contours.py` to `util_detect_eddies.py` since these
functions are also used, or will also be used, elsewhere.

And thus make the script more general and robust. Immediate
motivation: use the script on result from test `Get_1_outerm`.

Rename k1 to `d_init`, `k_min` to `d_min`, `k_max` to
`d_max`. Continuing the change in commit fdd8a7ea. k would be for date
index rather than number of days since 1950-1-1. As a consequence, we
also change option `-k` to `-d`, and we remove the short option for
`--dashed`.

From directory Analysis. Extract corresponding tests from
`Analysis/tests.json` into new file `Inst_eddies/Analysis/tests.json`.

k would be for date index rather than number of days since 1950-1-1.

Make them equal to basenames of shapefiles. Clearer and allows a
little simplification in programming.

There may be a fourth shapefile for centers of eddies.

A record is not a dictionary. The bug comes from commit 1431d67b.

This occurs when we read results from the Matlab program.

The bug occurred when: `args.anim` is None; `shp_tr_dir` contains a
file `ishape_last.txt`; `ishape_last.txt` contains a single
value (there is a single date in `shp_tr_dir`). Then loadtxt without
the argument ndmin return a numpy scalar. Then we cannot call
`len(ishape_last)`, at line 286.

The bug comes from commit fb9652fb.

Useful for automated test. See also commit 92bc155d.

Replace `reader_extr`, `reader_outer`, `reader_m_s` by dictionary
readers. Clearer and more concise.

Motivation: ease plotting of several snapshots coming from different
triplets of shapefiles, on the same figure. We may want to do this if
we have anticyclones and cyclones in separated triplets of shapefiles.

In order to extract the code for this function from the main part of
the script, we have to modify the behaviour of the script a little:
when the file `ishape_last.txt` could not be read or there is a single
value in it then args.k, if not None, must be equal to k1, instead of
being ignored.

In `make_animation`, when window is defined, use window instead of
computing bbox. Avoiding projection issues.

Bug from commit 04cef827.

Put existing code into new function `in_window` because we also want
to use it in another script: `plot_traj.py`.

In some use cases, we would rather not overwrite the title. For
example, if we overlap eddies at several dates, we may want to keep
the first date. Argument k was only used for the title. It is also
clearer not to have k as an argument because it did not select the
eddies plotted, the selection is made by argument `ishape_list`.

The script can plot more than a snapshot.

The repeat option does not work. Apparently a Matplotlib bug.

Bring plotting commands together at the end of the main part of the script.