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.

function A = spdiag(a,i)
    n = length(a)-abs(i);
    A = spdiags(a,i,n,n);
end