Mesh creation

[GiancarloMCorrea]

Hi,

I have been exploring alternative ways of creating a mesh in FishStatUtils/VAST. Currently, FishStatUtils allows the user to pass mesh arguments to the inla.mesh.create function through make_spatial_info. However, it is hard to explore what arguments we should pass if we cannot see the actual points creating the mesh (loc_i, loc_x). I have three main suggestions here:

1. Currently, make_spatial_info also allows users to pass a mesh when fine_scale = FALSE, but not when fine_scale = TRUE. Is there any reason for this?

2. I have created a function that takes mainly the first part of make_spatial_info testFunctionMesh.txt
   This function allows getting loc_x, loc_i, and loc_g. Moreover, it allows using the INLA::meshbuilder function if it is desired. Eventually, this function would be added to FishStatsUtils.

3. I also made an example to show this feature. It is important to implement 1) first. If not, it would only work when fine_scale = FALSE
   MeshCreation_example.txt

I hope this can help. This can be improved with future codes to plot mesh and points.

Giancarlo.