* Not re-exporting SpaceSetObject outside of the crate
* Removed unused SpaceObject definition
* Factored out Point definition.
* Remove `pub` visibility on definition not actually requiring it.
* Added an assert for indexing into a Position, in the case where the
position has only one dimension, the index MUST BE 0.
* Commented `highest_resolution()` as this is not yet used.
This prevents using references and forces extra allocations during
queries as we have to adapt the values.
Also remove is_empty() as it si currently unused, and needs to be
adapted.
* Refactor the index scale selection.
* Document more explicitly where coordinates are encoded or not.
* Improve error messages part of the encoding / decoding and of space
projections.
* Push down the parameters in order for filtering to be done as early
as possible w.r.t the view port.
* Add view_port-based filtering in the lower-layers of the DB.
* Implement PartialOrd on Position, to simplify point in box checks.
* Implement multi-scale indices generation.
* Deduplicate values before sorting them while generating an index, to
reduce the number of points to sort.
* Use a hastable to deduplicate values, instead of a sort + dedup call.
* Minor code cleanups
