Grid boundary specification

[kshedstrom]

I started on the road to generate a grid for the supercritical problem via gridgen when I remembered:

• In Seagrid, the boundary you provide ends up going through the first round of halo T-points, not the edge of the computational domain.
• In pyroms gridgen, the boundary you provide ends up going through the first round of halo q-points, even farther from the computational domain.

Since this is being revisited, can I please (please???) have a tool in which the boundary I provide goes along the edge of the computational domain? Anything needed outside can be generated by extrapolating.