add missing :cpp: formatter

to the solver (see :ref:`Chap:InputsMultigrid`).

NOTE: If either the :cpp:`nodal_proj` or :cpp:`mac_proj` bottom solvers are 

set to :cpp:`hypre`, the default behavior is to set the `hypre_namespace = "hypre"`. 

set to :cpp:`hypre`, the default behavior is to set the :cpp:`hypre_namespace = "hypre"`. 

In that case, the settings below should be preceded by the (default) hypre namespace, 

:cpp:`hypre`, and apply to either or all solvers which use hypre. However, 

the hypre namespace can be set at the solver level so that the hypre settings