Ep3: Be sure to close figures before running script

[gcapes]

Leaving the subplot figure window open confuses the output of the script.
Mention MATLAB's behaviour of reusing figure windows, and perhaps use the figure command right from the initial script to ensure we're plotting into a new figure.

[gcapes]

This could be fixed starting in the scripts episode. Rationale is that when running the script, we won't necessarily know if there are any open windows. To avoid unexpected results by reusing the top figure window, we'll create a new one using figure.