Preparing for more complex association criterium.

Because we are going to complicate the criterium of association
between two eddies.

Because we are going to introduce another variable for the
intersection of outermost contours.

Use out_cont%closed instead.

Remove dummy arguments nlon, nlat, periodic, `dist_lim` of
procedure `overlap`, use module variables instead.

Instead of using a literal constant.

It is not used and it complicates processing the edgelist.

Since `NR_util` has been integrated into Jumble.

We are reverting commit e48b7f7e. I think I did not really appreciate
then that the number of days since 1950-1-1 is another date index. It
is clearer to use just one date index, which is in the dbf files. So,
in effect, we replace everywhere the old 0-based date index k by `k -
d_init`. Note that we no longer need argument `d_init` for procedure
`dispatch_snapshot` and we no longer need to write `d_init` to file
`node_id_param.json`. Note also that the value of every node index
changes by the amount `d_init * e_overestim`.

Rename component `list_vis` of derived type snapshot to list. Since
there are no longer invisible (interpolated) eddies.

Remove test on orientation in `candidate_overlap`. This is useless
since commit 70e88286. We process an SHPC containing a single orientation.

Rename component `number_vis_extr` of derived type snapshot to
`number_extr`. Since there is no longer another compoment including
interpolated eddies.

The procedure does not exist any longer.

Write node indices instead of dates and eddy indices in
edgelist. Compute `e_overestim` from `ishape_last`. Remove header
lines of edgelist. See commit 3370733a. Replace argument d of procedure
overlap by arguments `e_overestim` and k.

Remove component `number_eddies` of derived type snapshot. It was the
same as `number_vis_extr` since there are no interpolated eddies any longer.

In procedure overlap, write an edge across delta days instead of delta
edges across single days. So we do not need procedure `write_overlap`
any longer, nor program `test_write_overlap`.

This is a big change, a big simplification. Creating interpolated
eddies was the way of Alexis Chaigneau. Rémi L. thinks it is no longer
useful.

So remove procedure `init_interpolated_eddy`; do not create SHPC for
interpolated eddies in programs `eddy_graph`, `test_overlap` and
`test_write_overlap`; remove argument `hshp_interp` of procedure
overlap; remove arguments `hshp_interp`, m, cyclone, `coord_extr_1`,
`ssh_extr_1`, `coord_extr_2` and `ssh_extr_2` of procedure
`write_overlap`.

Rename triplet to collection, `shp_tr` to shpc, shpt to shpc in
comments, identifiers and file names.

Also split the tests, Fortran source files, Python files and JSon
files. Keep at the top level the files used in both `Inst_eddies` and
Overlap.

Motivations for the split:

- The top directory contained many files.

- It may be useful to compile only one of the two sub-projects. For
example, only `Inst_eddies` on Ciclad, where MPI 3 is not available.

`unit_edgelist` was just transmitted by procedure overlap from main
program unit to `write_overlap`. So now overlap does not see
`unit_edgelist`. Further motivation: we are going to split the edge
list file into two files.

Improve clarity. The corresponding actual argument in `eddy_graph` is
`hshp_interp`.

To circumvent bug 98433 of gfortran.

Add main program `eddy_graph`.

Change order of dummy arguments of `dispatch_snapshot` and overlap.

Rename files and identifiers: change `"shp_triplet"` to `"shp_tr"`.

Create derived type `shp_triplet`. Motivation: we need to manipulate
two triplets of shapefiles in program `eddy_graph`. Use everywhere a
variable of type `shp_triplet` instead of the three variables
`hshp_extremum`, `hshp_outermost`, `hshp_max_speed` when all three of
them appear. Rename character variable `shp_triplet` to
`shp_triplet_dir`.

Add possiblity of specifying `delta_in` and `delta_out` in program
`test_overlap`.

Bug fix in procedure overlap: `delta_out` and `delta_in` should not increase.

Change the order of dummy arguments of `write_overlap`.

Add tests for program `test_write_overlap`. In program
`test_write_overlap`, make the eddy identifiers distinct.