Chapter 6 added fig 6.4 & 6.5

I also included a version of plot 6.5 using rCharts, which allows you to toggle off the countries and view the data values / legend interactively. If we are ok adding rCharts to the list of dependencies then I would like to remake more of the plots in this framework.

![screen shot 2014-07-01 at 11 17 34 pm](https://cloud.githubusercontent.com/assets/4986513/3451453/7a95fc2e-0197-11e4-8137-ef41ad4bc26d.png)