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.

% Prints the version and location of the sbplib currently in use.
function sbplibVersion()
    scriptname  = mfilename('fullpath');
    [folder,~,~] = fileparts(scriptname);

    name = 'sbplib';
    ver = '0.0.x';

    fprintf('%s %s\n', name, ver);
    fprintf('Running in:\n%s\n',folder);
end