All the GIGS JSON files have been converted to the gie format
and are now covered by running "make check". Therefore we no
longer need the Python setup. Removing it from the Travis CI
setup should speed up the test execution time a bit.

Central conic projection implemented as 'ccon'.

Use NumPy functions a bit more and avoid using np.append too much.
The previous code did not ensure that interpolated points were less than
the tolerance apart.

Otherwise, it will try to use pre-installed data instead of a local
copy.

Plotting script is now more flexible and makes it possible to do more
elaborate setup of each individual plot. This is done by adding a JSON
file that holds a record for each plot in the documentation. A plot
can now be restricted to a given bounding box, and there's a choice
between plotting as polygons or linestrings, as well as both low and
medium resolution data to go choose from.

Plots have not been added to the repository yet, they will show up in
a later commit although most of the work is done here. Most
plots are now done as polygons. Generally speaking the plots that are
still based on line data have show some problems when plotted as
polygons. There is still an unsolved wrap-around problem that should
eventually be fixed.
The land.geosjson dataset has been densified manually at the antartic
to make sure that the land mass is depicted correctly in projected
space.