Basic Highcharts support

Adds a new possibility: Highcharts!

```ruby
push.highchart(
  [ {name: "Series 1", data: [1,2,3,4, 6.5]} , {name: "Series 2", data: [7.5, 2.2, 1]} ], {
  title: { text: "Some neat chart" },
  yAxis: {
    title: { text: "This is the Y-Axis label" }
  }
})
```