TODOs:
stroke
styling on barsData about percent change of flights movement by entity (Jan - Feb 2016 vs Jan - Feb 2015) from PRU website.
Inspired by Mike's Bar Chart with Negative Values.
forked from espinielli's block: Flights by entity (Jan - Feb 2016 vs Jan - Feb 2015)
https://d3js.org/d3.v3.min.js