Key in Morton index (Z-order)

[szaghi]

The key_abstract will have some concrete extensions, e.g. a simple integer key or a simple string one. However, I'll need a more powerfull type of key, the Morton's index that allows for the Z-ordered space in 2D/3D: it has many good features for quadtree/octree implementations. Here the list of some references:

• old OFF implementation
• morton_fortran
• libmorton
• wikipedia
• Morton bit interleaving
• algorithms comparison

[szaghi]

Created a devoted project here.