[partition] fix divide_box free function which was not inline...
[partition] remove unused types, make level size_t
[partition] add condition in handle-functions for future improvements (next commits)
[partition] enhance performance of partition where substantial part of one
or both collections are exceeding the separation line. Formerly they were
always handled quadraticly. Now they are partitioned as well.
Merge branch 'develop' of github.com:boostorg/geometry into develop