Add a function to draw ellipses, rectangles and closed polygons

[sboeser]

For ellipses, the most "practical" inputs for the users are probably

• x,y of center
• length of the two semi-axis (i.e. radii). Set r2 = r1 to draw a circle if r2 is not given?
• angle of first semi-axis with respect to horirzontal

Rectangles are typically just

• x1,y1 for one corner
• x2,y2 for the other corner

Closed polygons are of minor importance, but - depending on whats available in d3, the best way to get a circle might be a polygon?

[sboeser]

https://bugs.icecube.wisc.edu/view.php?id=6810