message: more specific imports
diff: extern crate argmin;
  extern crate ndarray;
  use argmin::prelude::*;
  -use argmin::solver::newton::*;
  +use argmin::solver::newton::Newton;
  use argmin::testfunctions::{rosenbrock_2d, rosenbrock_2d_derivative, rosenbrock_2d_hessian};
  use ndarray::{Array, Array1, Array2};
  