Also split the tests, Fortran source files, Python files and JSon
files. Keep at the top level the files used in both `Inst_eddies` and
Overlap.

Motivations for the split:

- The top directory contained many files.

- It may be useful to compile only one of the two sub-projects. For
example, only `Inst_eddies` on Ciclad, where MPI 3 is not available.

spherical_polygon_area to spher_polygon_area.

In procedure max_speed_contour_ssh, instead of aborting when the speed
is not defined, continue with missing_ssh. Found such a case in
November 29th, 2015 data. Added corresponding test. In procedure
set_max_speed, if max_speed_contour_ssh returns missing_ssh then we
just take the outermost contour as max-speed contour.

order to take missing value attribute into account.

For ssh, missing value is huge(0.). We have to take a large value
because Contour_531 has an argument zmax for missing values. For
velocity, missing value is a quiet NaN. We have to take this because
we need to know if the interpolation procedure in mean_speed has not
used any missing value and we do not want to alter the interpolation
procedure itself.

In local_extrema, we accept as local extrema only points with 8 valid
values around them.

When we look for the maximum speed contour, we are hoping that good
contours do not englobe missing values. If this happens, the program
aborts.

When computing the mean speed on a contour, we are hoping that the
interpolation of speed on contour points does not use missing
values. If this happens, the program aborts.

Draw coastlines in plot_snaphot.py. At the same time, this allows the
use of any projection.

input depending on noise_around. So it is clearer to compute radius
outside of max_speed_contour_ssh. Thus, we simplify
max_speed_contour_ssh. radius is an input argument. The case where
radius == 1 must now be processed also outside of
max_speed_contour_ssh.