Adaptive mesh density

[nwpointer]

using a BTree + based longest edge subdivision would allow for dynamically controlling mesh density either by distance from camera or some other criteria while avoiding gaps caused by T-junctions in quad-tree based solutions.

[nwpointer]

got a basic cpu based B-tree working

[nwpointer]

Initial attempts were not fast enough to recalculate the mesh as the camera moved around or had other draw backs like visible 'pop-in' as geometry detail increased so I've not merged them into main.