Snap to start point if last segment

I'm not sure if what I added here is the desired result or not, so feel free to ignore. I wanted to make a bunch of triangles and noticed that I never could quite get that because of the order of drawing lines and closing the polygon would always draw a fourth segment. This "snaps" the last vertex to the start vertex if it's within 10px.

I really enjoyed the latest installment of vart.institute and thanks for creating this! :+1: 

![tri](https://cloud.githubusercontent.com/assets/220341/5023659/f4e7c1e6-6aca-11e4-83b4-ce27b09af1dd.png)