API: merged 'set_params' and 'get_params' into 'settings'
added a 'settings' method to 'BaseSupervisedPredictor' for consistency + 'settings' doc improvements
DOC: update with the new 'settings' method
removed empty lines from '__str__' output
pep8 fixes
added a 'settings' method to 'BasePredictor'
API: 'learn' methods now return the predictor itself