Implement 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 ratings-based recommendations
Merge branch 'master' of github.com:ntnu-smartmedia/elephant

# By Patrick Romstad
# Via Patrick Romstad
* 'master' of github.com:ntnu-smartmedia/elephant:
  Added similarity based recommendation