* New nodes are first linked before adding them to the lane. This avoids using invalid lane end positions.
  * In the get_start_point() and get_end_point() functions: the lane object address is compared instead of the lane ID.
  * In the get_start_point() and get_end_point() functions: for left lanes, the last node is used instead of the first one to get the desired point.

Completed the feature to copy the whole structure and update the references.

Added a function to return the length of a lane.
Solved a bug with the names of the road marks.
Solved a bug when kinking two nodes in the same lane.

Road nodes from diferent roads at the same location are fused.
Road nodes can belong to multiple lanes: each has a vector of parent lanes and geometries.

Added support to link road segments.

TO DO: add the functions to link road segments.