Beginning work on car_crashes example

 - Interactive graph of data from 538 blog post about car crash
   statistics by state,
   http://fivethirtyeight.com/datalab/which-state-has-the-worst-drivers/
data2json.R: add rank info
Initial stab at figure, with just top panels
top panel: each has x-axis label (they _do_ fit)
car_crashes: put car_crashes.js in .gitignore