Which is separate for cyclones and anticyclones. For now. Then we do
not need the argument cyclone of functions `convert_id` and
`print_edgelist`, and we do not need to read `Nanti.mat` for
processing cyclones.

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.

Preparing for a fourth shapefile containing centers.

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.

Remove fields interpolat, cyclone and valid from `extremum.dbf` and
field radius4 from `outermost_contour.dbf`. For now, we just want to
change the format of Matlab results, not add to the contents.

Read the path to first file and the last date from the command line.

Take into account renaming of files in f7075db7 and moving to new
directory in 125569d8.

`inst_eddies`: instantaneous eddies. `overlap`: overlapping.

Better than the generic `convert_Matlab_v6.sh` because we do not need
all the variables of file `adt....mat`.

The bug comes from commit fb9652fb.

So we do not read the name of input `.mat` files from the command
line, we assume they follow a pattern, and we need the files to be
present in the current directory. Also, since the dates are specified
in the script, we check that each date is equal to the date stored
inside the corresponding `.mat` file.

Preparing for the loop on dates. The mat files will be open inside the
loop which will output shapes, so the output of namelist, which use
mat data will need to be after.

Separate the definition of the fields of shapefiles and the output of
the namelist from the output of the shapes. This will allow us to loop
on dates only for the output of the shapes. Create two sets of writers
so that we will be able to alternate between the two sets when we loop
on multiple dates. So we create a function `define_fields`, we replace
the argument `SHP_triplet` of function write by argument writers and
we create the dictionary factories.

This allows to run `plot_eddy_contours.py` on the results.