Write file `node_id_param.json` from programs `test_overlap` and `eddy_graph`.

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.

Do not create file `number_eddies.csv` in program `eddy_graph`. Since
there are no interpolated eddies any longer, the file
`number_eddies.csv` just contained the same information that is in
`ishape_last.txt` in the input SHPC. Remove argument
`unit_number_eddies` of procedure `dispatch_snapshot`.

Do not create attribute interpolat of nodes in graph. There are no
longer nodes that should be drawn with a box.

No longer useful since there are no interpolated eddies any longer.

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

Thus remove too component interpolated of derived type eddy and
component `extr_interp` of derived type shpc.

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`.

Do not try to read attributes of interpolated eddies when reading a
graph. Remove option `--interp` of scripts `report_graph.py` and
`report_graph_int.py`. Remove argument `read_interp` of function
`read_eddy_graph` in both scripts.

As the namelist is now shorter, it is no longer convenient to write it
into a file.

Remove tests `Write_overlap_different` and `Write_overlap_shifting`:
they are no longer different from test `Write_non_successive_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`.

Consequence of commit 664f62bb.

Redefine `k_test_[12]` as date indices (0-based) instead of dates.

Follow-up to commit 3b68dd5.

Follow-up to commit 3b68dd5. A default value of 0 for k in main
program unit `test_get_dispatch_snap` now makes sense.

This does not make the code simpler but a little more general,
anticipating for example time steps different than one day.

In main program unit `eddy_graph` and procedures `dispatch_snapshot`
and `read_snapshot`, variable k now refers to the date index, 0-based,
instead of the date in days since 1950-1-1.

In main program unit `eddy_graph`, add variable d for date. `k_begin`,
`k_end` and `k_end_main_loop` also now refer to date indices. We have
to pass an additional argument `d_init` to procedure
`dispatch_snapshot`.

Note that no modification is necessary in procedures `get_snapshot`,
`recv_snapshot` and `send_snapshot` although the meaning of k in
`get_snapshot` and tag in `recv_snapshot` and `send_snapshot` also
changes.

Replace positional argument template by optional argument. This
argument is now needed only in case we process several dates, since
the first date is now read from the NetCDF file.

The script may abort because of wrong arguments. It is better not to
have touched anything in that case.

Following commit 4792f83f.

To ease use of call with keywords.

Even for a run with a single MPI process, otherwise execution will not
work on some systems (jean-zay).