In Curve: Added numerical FD differentiation if derivative is not supplied. Added arc length computation based on the derivative. Added arc length parameterization (but this function is very slow.). In +util: Added fzero_vec.m and integral_vec.m, which call fzero and integral but take vector arguments.

% Plots all the eigen values for a sparse matrix.
function plotEig(A)
    e = eig(full(A));
    e = sort(e);
    plot(e,'.')
end