Add tests for elo

* Test for EloCalculator
* Test for ScoreValueCalculator
* Test for ExpectedScoreCaclulator
* Test for TrasformedRatingCalculator
![tumblr_ltq0ldzibe1r19y5ho1_250](https://cloud.githubusercontent.com/assets/755201/5445006/1f60a34e-847e-11e4-9135-c88c4d5be85d.gif)