Feature/feature hasher

FeatureHasher added as an alternative to DictVectorizer.

Added 2 parameters in config file in Input part:

* feature_hasher = true, could be true or false. By default it is False (works as DictVectorizer)
* hasher_features = 5 (Number of features used in the feature_hasher, at least should be the number of features among all files.)

`nro_features` is not a very clear name to me. How about `num_features` for the parameter name?