neighbours function should not return the center cell itself

[tboch]

This is not really a bug, but it is surprising that a neighbours function returns by default the cell given as parameter.

[ManonMarchand]

Proposition to change this:

• rename neighbors into neighborhood and propagate to functions that depend on it
• create a new neighbors that return the expected output

as it is an API change, we would need to first publish a warning in the next version (0.7?), and then deprecate in the version after that (0.8 or 1?). Or we do that in the 1.0.0 directly?

[ManonMarchand]

Note: there is a boolean on rust side to remove center