Candidate for Drop 2

I couldn't quite get this syntax to work for plotting vertical lines at projected finish sprint:

                        xAxis: {
                            categories: chart_hash.Name,
                            plotLines: [
                                {
                                    color: '#000',
                                    width: 2,
                                    value: this._target_backlog
                                }
                            ]
                        },

So I somewhat clunkily add an additional thin column denoting the projected finish at that sprint. However it renders side-by-side with the velocity columns, so it's a bit unwieldy. Maybe you can figure out what I'm doing wrong. Also - only one sprint completed so far in "A Release 2" so best/worst velocities are currently the same.
![screenshot1](https://f.cloud.github.com/assets/1858223/1027332/539385ae-0e6f-11e3-8d1a-df28837c6713.png)