Added Fixed Duration Series

[travisbeck]

I wanted my graphs to be able to be listening on a page indefinitely, so I took the liberty of writing a Rickshaw.Series.FixedDuration class. It expects consumers to send timeInterval and maxDataPoints, otherwise it should be a drop in replacement for Rickshaw.Series.

I had to refactor Rickshaw.Series a bit to get it to want to be subclassed.

[Jae]

I had to change Makefile to include 'src/js/Rickshaw.Series.FixedDuration.js' could this be done?

[davidmontgom]

Is there any documentation on how to do realtime steaming? I can not get realtime to work. Random sample does not explain how to use real word ajax updates. How do I fix the below?
data = {cpuUsage:[{y: 0.999, x: 1362914221}]};
graph.series.addData(data);
graph.update();