Module implementing index-reorder functionality for grids.
! 2020-03-10 Chichi Lalescu:
! In this module functionality related to the mesh%reorder method is put together.
! The basic pieces are the functions for computing the 2D Morton z-index, i.e. functions for
! bit interleaving and appropriate bit masks.
! On top of that the method Morton_2D_shuffle_block adds the ability to assign Morton z-indices
! to square blocks rather than single grid nodes, which should provide much better options of
! cache-access optimization.
!
! 2020-01-10 Chichi Lalescu:
! In this module I'm putting together functionality related to the mesh%reorder method.
! While I am starting with a Morton z-index, I believe in the future we will need to do something
! slightly smarter, hence I think it's best to have this space dedicated to that.