[read_wkt] Don't append duplicated, closing Points in open Rings/Polygons.

Note that Points are still appended if there is not enough Points in the input, i.e. the number is < 3 for open Rings.
[test] Update tests to be in line with the change in behavior of read_wkt() for open Rings.
[test] Remove temporary/unneeded code in point_iterator test.
[from_wkt] Move the appending logic outside container_appender and dispatch by closure.
[from_wkt] Add default template parameters to parsing_assigner.
Merge branch 'develop' into fix/read_wkt
Merge branch 'develop' into fix/read_wkt
[read_wkt] Remove unnecessary remove_reference usage.
Merge branch 'develop' into fix/read_wkt
[buffer][performance] add boolean to indicate concave rings:
in non concave rings, no turn calculation is necessary
[buffer] reverse negative rings if necessary (for concave pieces and
one-sided buffers)
Merge branch 'develop' of github.com:boostorg/geometry into develop
[buffer][test] enhance display of pieces
[buffer] fix error in comment
[buffer] small change, use Piece i.o. typename ....
[buffer] major fix: we now create concave helper-pieces differently
In the past there was one with a straight line going from one piece to the next.
Now there are two, going from one piece to the point on the geometry, and the
second going from the point on the geomety to the next piece.
They are now zero-volume.
They fix:
1) crossings of sides with flat-ends (unit-test cases curve, field_sprayer, bend_near_start)
2) joins with limited number of points (unit-test cases concave_b_rough, italy_part, nl_part)
3) joins with large distances
4) many self-intersections on remaining aimes-cases
[buffer][test] added unit test using large country multi_polygons
This one is not enabled by default.
Aimes-test is no enabled by default
[core] Add sphere and spheroid reference models.

Add new tags for reference sphere/spheroid concepts.
Add cs::model::sphere<> and cs::model::spheroid<>.
Add get_radius(), set_radius() and radius_type<> functions/metafunctions.

Add tests.

Refactor [extensions] nsphere to use the official functions.
[extensions] Use Spheroid in andoyer and vincenty strategies.

Replace RadiusType template parameter of those strategies with Spheroid.
Replace member function radius() with model() and typedef radius_type with
model_type.
Use get_radius(), calculate flattening "manually".
Tweek calculations (conversion warnings, common multiplier).
Remove detail::ellipsoid<>.
[index] Remove unneeded file.