features that would be nice to add

[gaelforget]

these would be welcome contributions :

• port gcmfaces_remap_2d.m and gcmfaces_remap_3d.m to support remapping from regular grid to any grid supported by MeshArrays.jl
• port layers_remap.m that remaps to arbitrary vertical grid
• port diffsmooth2D_extrap_inv.m and diffsmooth2D_extrap_fwd.m to allow for gap filling via diffusion approach