small cleaning up of load_features in features_utils and read_features in utils. made read_features require a max_year and day. added strictness to load_features. has assert that requires max year and day are in the years and days list. we could relax this but seems better to be safe and strict for now. we are also strict about the feature dict we get back from read_features. we assert that this contains no year or day that we did not ask for in the years or days list.