Added the calculate_similarity function to module fourcity_clusterer. The function uses euclidean, cosine, and pearson similarities
Added support to pass the similarity metric as a parameter for the SingleCF recommender class
Added the BaseRecommender class, which is necessary to run the SingleCF recommender. This class will be modified or removed in the future
Added a couple of functions to automate the execution of several recommender systems
Created four new recommender systems based in multi-criteria ratings
Updated the multi-criteria recommender systems so now they all extend de MultiCriteriaBaseRecommender class