Removed the trim to range functionality, since is not part of the recommender system, but is something than can be done after the rating has been predicted
Created a couple of classes to measure the mean absolute error and the root mean square error
Removed some unused variables in this class
Removed some unused functions from fourcity_clusterer module
Made some improvements in the management of variables in the MultiCriteriaBaseRecommender class and its subclasses
Created tests for the ETLUtils class and the similarity module
Created unit tests for the MeanAbsoluteError class and the RootMeanSquareError class
Created tests for the SingleCF class and the ReviewsHolder class
Created tests for the DeltaRecommender and the OverallRecommender classes