[index][example] Improve the rtree visualization.

Add support for rtrees storing Points and Segments.
Add the support for Segments in print_indexable() and gl_draw_indexable() index utilities.
Merge branch 'develop' of github.com:boostorg/geometry into develop
[doc] Add info about Segments Indexables and more pictures.
[doc/index] Updated example rtree pack creation time, after optimization.
[doc/index] Compact the new knn query pictures. Add knn code snippet.
Merge pull request #33 from mkaravel/develop

[distance] fix bug in point-box distance computation in range-to-segment/box code
[test][distance L/A] add two seg-box test cases provided by Adam Wulkiewicz
[test][distance] in the case of the segment-box combination,
also test output with respect to the generic algorithm that first
checks for intersection, and if that fails, checks all possible
point-segment combinations of the segment and and the box
[distance] modify the point-to-range code so that a container/range
of points can be passed as an argument (e.g., a vector of points)
[distance] modify the range-to-segment/box code, so that in the case
of computing the distance of a point of the range from the box, the
point-to-range code in point_in_geometry.hpp is used
[distance] fix bugs in segment-to-box distance computation;
add generic algorithm for computing segment-to-box distances:
the algorithm first checks the segment and the box for intersection,
then if no intersection is found, it returns the minimum distance
over all point-segment combinations from the two geometries; for
computing a point-box distance the algorithm either calls the default
point-box strategy, or calls the detail::distance::point_to_range
algorithm; this alternate segment-box distance computation algorithm
is currently used in unit tests of segment-box distances to verify
results with the cartesian-specific approach
Merge pull request #34 from mkaravel/feature/distance

Feature/distance
[example/index] Fix GCC/clang c++98 compilation error in glut_vis.cpp

The error is caused by the Boost.Move limitation - the correct implicit assignment operator can't be automatically generated for a containing class.
[doc][wkt] Fixed WKT doc / extended WKT doc (in progress)