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.

% Choose the number of points on m, M, so that the step size is equal to that for N points on n.
function [M] = equal_step_size(n,N,m)
    M = round((m*(N-1)+n)/n);
end