Contours serializing

Note: incorporates contours-hierarchy

So I needed methods for easy access of the data (mostly because of https://github.com/peterbraden/node-opencv/issues/171). But this also allows you to save contour data for later and use it to draw. I guess you could even generate shapes in JS and load em in, although i dont know how efficient or wise that is.

Also I added a Points(pos) that gives you all points, much handier. Cheerio!