Histogram charts

Use Case: To show the relative distribution of values I would like to display my data in an [histogram chart](http://de.wikipedia.org/wiki/Histogramm)

While a histogram chart _looks_ just like a bar chart, raw data can’t be just used to display an histogram of this data – so called »binning« must take place before (answering the question »how is it different from a regular bar-chart« in #586) .

(I tried to just use the [d3.layout.histogram()](https://github.com/mbostock/d3/wiki/Histogram-Layout) to do these calculations before using a simple c3 bar chart, but I was unsuccessful with this approach)