Function grid_trait::grid2::mut_fn

pub fn mut_fn<'a, I, T, F>(f: F) -> KolmoMutGrid2<'a, F, I, T> where
    I: From<Vector2<i32>>,
    T: 'a,
    F: Fn(I) -> &'a mut T, 

Represent a coord → &mut Item function as a grid.