POD update: Add setq() and setq_option() to Script, and add set_option($options) usage to Dataset. That way, the two modules have almost the same interface about options.
POD update: Script: now plot() accepts only string or object. it does not accept arrays because it causes confusion if we have plot_with() method, which takes named params. named param "dataset" => $dataset would accept a single dataset and an array of dataset, but if dataset itself was an array, it would be very confusing.