1.4.3

• Fast rebuild of the MPI AMG hierarchy in case the system matrix structure has not changed.
• Support block valued backends with smoothed aggregation coarsening when user provides near nullspace components. This is implemented with help of hybrid backends, relaxation::as_block, and coarsening::as_scalar. See the "Using near null-space components" tutorial for more details.
• Implement backend::reinterpret_as_rhs() helper function for easy reinterpretation of scalar vectors as block-valued.
• Support complex types in MPI solvers.
• Minor improvements and bug fixes.