Chapter 8 example

Hi,

I was interested in using Quil to create network graphics.  After I bought Fry's *Visualizing Data*, I found your Quil translations of chapters 3-7 helpful.  I decided to try translating Fry's force layout code from Chapter 8.  I got a minimal version working.  Feel free to incorporate it into your repository if you'd like.  

I didn't try to match the stylistic decisions in your code.  For example, I used Quil's functional mode.  

I found it a bit difficult to make Fry's force layout code into a purely functional style, but eventually succeeded by taking liberties with the organization of the code.  That is, it's more of a rewrite than a translation.  (Nevertheless, I'd guess a force layout algorithm implemented in Clojure from the start, by someone who understood how it works, would be simpler.  Fry never explained the principles of his force layout code, and I didn't do the research to figure it out.  I just tried to reproduce the same mathematical effects.)