Remove dummy arguments nlon, nlat, copy of procedure `recv_snapshot`,
use module variables instead.

Remove dummy argument `max_delta` of procedure `dispatch_snapshot`,
use module variable instead.

Remove dummy arguments nlon, nlat, corner, step of procedure
`read_snapshot`, use module variables instead. Note that we keep copy
as a dummy argument instead of using the variable of module
`config_graph_m`, because we want the procedure `read_snapshot` to be
usable outside of the `eddy_graph` program.

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

Remove dummy arguments nlon, nlat, corner, step, copy, `max_delta` of
procedure `get_snapshot`, use module variables instead.

Add `config_graph.f90`and `read_grid.F90` to lists of source files.

Which read namelists. Motivations: diminish the number of arguments of
procedure overlap; lighten the main program unit. We conditionally
compile MPI calls in `read_grid` because we want to use variables of
module`read_grid_m` in procedure `read_snapshot`, and `read_snapshot`
is called from sequential program `test_nearby_extr`.

This is a bug from commit b2ee6af5.

If segments were not in graph order in `traj_segm.json` then
`draw_segments.py` would have to sort them after reading them. That
would be possible but it is better to create directly trajectories in
graph order in `trajectories.py`, as there is probably no time penalty
for this.

So we can print the error message from NCO, which is in standard
output. This is particularly useful when the longitude range specified
by xmin, xmax is not valid.

Instead of using a literal constant.

Superceded by class `SHPC_class`.

Rename test `Plot_eddy_contours_wind` to
`Plot_eddy_contours_window`. `wind` is misleading.

Use a dictionary instead of a list for `ishape_lists_all`. Thus we
avoid the need to remember that the first item corresponds to
"Anticyclones" and we avoid the awkward `zip(ishape_lists_all,
["Anticyclones", "Cyclones"])`.

The immediate motivation comes from tests `Mat_v6_to_shapefiles` and
`Plot_eddy_contours_Mat`. `Plot_eddy_contours_Mat` needs to open the
SHPC in `Mat_v6_to_shapefiles`. `Mat_v6_to_shapefiles` does not create
`n_slices.txt` and we do not want to create `n_slices.txt` in
`inst_eddies_v6.py` because this script could be run in parallel for
several slices. There is no simple way to create `n_slices.txt`
automatically after runnning `inst_eddies_v6.py` in the test
`Mat_v6_to_shapefiles`. We cannot use a redirection in a command of
the test so something like `echo 0 > n_slices.txt` would not work.

Note that orientation = None is passed to `get_ishape_last` where it
becomes `self.def_orient`.

Move function `comp_ishape` to method of SHPC class.