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).

Replace `/proju/lmd-oce/data/AVISO/DT_2018/2006/01` by
`$large_input_dir`.

Move the definition of colors out of the loop on shapes, since the
orientation is now the same for all shapes.

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

Clearer for the user.

`h_region_1.nc` is no longer in the repository, since commit d023fd3f.

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.

The orientation is no longer a DBF field.

Instead of `d_init`, `ishape_last` and `reader_extr`.

Instead of readers. Preparing for extension to receive orientation.

Instead of `readers_all`.

Instead of several pieces of it. Clearer and more concise.

Instead of several values of the handler dictionary. Clearer and more concise.

Instead of tuple. Preparing for extensions to return orientation and
to deal with several SHPC.