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.

To ease use of call with keywords.

Instead of `Inst_eddies_5`, which no longer exists because we now
create separate SHPC for each orientation.

This SHPC was made with an old version of `inst_eddies`: it contained
cyclones and anticyclones output together. We create a test `Region_6`
instead.

Because variables in `grid_nml` should be all defined in the input file.

With separated orientations.

We now impose that all eddies in an SHPC have the same
orientation. Remove field `extr_cycl` from the derived type shpc and
add field cyclone to shpc. When reading an eddy, give it the
orientation of its SHPC. Add argument cyclone to procedure
`shpc_create`. Create a file `orientation.txt` in each SHPC. When
writing an eddy, check that its orientation matches that of the SHPC.