Hxt refine dev
The main change is that the way we handle varying mesh size in the refinement was slightly wrong and has been updated.
I also tried to break "spire/needle" tetrahedra early, by inserting a line of point inside them, but it turned out to be slower because I created too many points that were going to be filtered out later in the process. Therefore, I reverted back to the main strategy with a new commit, because the git history could be of some use one day.