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.

% [x,h] = get_grid(a,b,m)
function [x,h] = get_grid(a,b,m)
    % TODO: allow the interval to be a vector
    x = linspace(a,b,m)';
    h = (b-a)/(m-1);
end