Add support for ellipse and circle

[sandeepmistry]

From @tigoe:

Add in graphics primitives: ellipse(), circle(), rect(), from Processing/p5.js
...
obviously ellipse() is the key one. circle is just a special case, and arc is less used, though useful for pie chart progress meters, I suppose.

[ashutoshshrm529]

I have written an ellipse function here - #9 (comment)

Since there is no examples subdirectory in this library, the checks could not run.
Could the moderators please look into it.
Thank you.