Interpolate from grid.

[pfebrer]

I would like to add a method to interpolate values from a Grid, given some coordinates. I have looked into it and it seems like the way to go is to use scipy.interpolate.RegularGridInterpolator.

To clarify, the method would work something like this:

rho = sisl.Grid(...)

# Get the value of the electronic density at the points that we are interested, even
# if they are not part of the grid.
interesting_points = [[0,1.3, 4.5], [2.3, 4.7, 10]]
rho_vals = rho.interpolate(interesting_points) 

(1) Do you think it makes sense? (2) Where would you put it, given that there is already a method named interp?