public static List<String> parseFlat(final String featureDir) throws IOException {
        return parseFlat(featureDir, Collections.emptyList());
    }
Parses features to a {@code List} of Gremlin strings.

@param featureDir The root directory where feature files can be found including subdirectories
gremlin-language/src/main/java/org/apache/tinkerpop/gremlin/language/corpus/FeatureReader.java