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.

% Concatenate two curves g1 and g2 intop
%   g = concat_curve(g1,g2)
function g = concat_curve(g1,g2)
    function v = g_fun(t)
        if t < 1/2
            v = g1(2*t);
        else
            v = g2(2*t-1);
        end
    end
    g = @g_fun;
end