cosmetic fix of ct_str_to_vls
overload + operator as intersect (brl-cad uses it with the same meaning)
add some needed defaults to wdb#combination method
fix shader param format (needs more wrapping, later)
Use factory method from_wdb to create primitives when reading from file
added Vector.transpose method; added X, Y, Z methods to get the unit axes;
WIP: fixed Transform/Vector multiplication
remove setting of region_id
added: hilbert_pipe.py example
Rewrite of the 2d hilbert curve example
added hilbert_3d.py to the examples
libert_3d example: extract params in a map to allow for variants