more tests to evaluate domain and fields b_cart and a_cart at 3d arrays which...

 more tests to evaluate domain and fields b_cart and a_cart at 3d arrays which are not meshgrids added, so a full 3d set of points. Pmap had to be fixed again (now more elegant with np.vectorize), all other parts did work correctly already. Modified docstring saying either 1d arrays or 3d arrays as input for the s,a1,a2 variables.