Add Machine Learning: PredictionIO Ruby SDK.

> PredictionIO is a prediction server for building smart applications. You can make
predictions through PredictionIO just as you would filter data using a database server.
>
> With PredictionIO, you can write apps
> * that predict user behaviors based on solid data science
> * using your choice of state-of-the-art machine learning algorithms
> * without worrying about scalability