Responds to a GET request to /feature/importance or /feature/importance/[feature number] . In the first case, the results are feature importance values for all features in order as specified in the configuration. In the second case, specified by number, the result is a single feature importance. In both cases, importance is given as a floating point value between 0 and 1 inclusive. Higher means more important. The values are normalized and are not expressed in particular units. The result contains one importance value per line. If JSON output is selected, the result is a JSON list of importance values.