Create skeleton code for SimpleKNN.get_rating()
Create evaluation package.

- Implement MAE, NMAE, MSE and RMSE.
- Skeleton code for cross validation.
Merge branch 'master' of github.com:ntnu-smartmedia/elephant

# By Patrick Romstad
# Via Patrick Romstad
* 'master' of github.com:ntnu-smartmedia/elephant:
  Added prettier print