fzero_vec, integral_vec and spline are now local functions in Curve. Renamed arcLengthStretch to arcLengthParametrization. Removed plot_derivative. Added some comments and extra lines + removed unneccesary lines. arcLength is now a method and not static. Constructor does not accept difference operator anymore.

function e = error2d(discr, v1, v2)
    % If v1 and v2 are more complex types, something like grid functions... Then we may use .getVectorFrom here!
    h = discr.h;
    e = sqrt(h.^2*sum((v1-v2).^2));
end