Adds multiple histograms side-by-side example

This example was an answer to [this StackOverflow post](http://stackoverflow.com/questions/25942703/multiple-side-by-side-histograms-with-matplotlib). It plots several histograms side by side; this helps compare several data sets for example.

Here is the output from the example:

![figure_1](https://cloud.githubusercontent.com/assets/1926734/4371551/350ac414-4319-11e4-971e-4110132c3ab5.png)