program behavior.

In plot_snapshot.py, no need to accumulate all content of shapefile
extremum_1, just process it record by record, as for other shapefiles.

namelist input. Also, choose name of primary NetCDF variable in
namelist and read only this variable, not its coordinates. This makes
it easier to use an arbitrary NetCDF file.

In program test_set_outermost_contour, it is hard to remember the
order of positional arguments so we rather use fixed input file names
and no arguments.

In JSON input file for tests, it is simpler to use the "input" key
than creating a one-line input file, in some cases.

defined. Also, allow test_set_outermost_contour to read ssh from a
NetCDF variable with a degenerate time coordinate or with no time
coordinante.

"stdout" key became optional in "tests.json" and "directory" key
became "title", with no indication of directory.

acceptable. So define flat_extr by a strict inequality in procedure
get_snapshot.

Procedure set_outermost_contour no longer has a dummy argument
noise_around. We no longer call outermost_possible_level so we do not
have an artificial discontinuity of results with and without maximum
amplitude. We abandon the idea of reducing the amplitude of initial
level_good compared to innermost_level: problem of consistence with
get_snapshot, and it does not seem worth the trouble, just abandon
those problematic extrema. Allow for null outermost_contour instead of
aborting.

In procedure get_snapshot, s%list_vis(i)%suff_amp is first defined
only if flat_extr(i). Also we are no longer sure that
set_outermost_contour finds an outermost contour so we have to test
this to define s%list_vis(i)%suff_amp. noise_around is now defined
only for flat_extr(i) and s%list_vis(i)%suff_amp. Also, since we may
not find an outermost contour even if not flat_extr(i), we update
s%extr_map after the second call to set_outermost_contour.

In procedure local_extrema, we use the mask diff_center instead of
mask_center. So we no longer need procedure construct_mask_center. In
procedure local_extrema, we ignore one in two adjacent degenerate
extrema instead of aborting.

In plot_snapshot.py, color extrema and allow for null outermost
contour.

Synthesize output in test_local_extrema.py.

sufficient amplitude.

low-amplitude threshold, min_amp.

Add component suff_amp to derived type eddy. Write this component in
extremum_$m.dbf.

In shapefiles, write positions of vertices in degrees rather than
radians.

test_get_snapshot reads the whole domain of input NetCDF files instead
of selecting a window through a namelist. This is clearer and more
convenient. Same in test_get_snapshot.py, test_local_extrema and
test_local_extrema.py.

In test_get_snapshot.py, annotate extrema instead of inserting a
legend.

More correct names: radian_per_degree to deg_over_rad,
degree_per_radian to rad_over_deg.

test_good_contour has more general input.

test_inside tests only inside, no loop on radius.