anchor.diff:        help: 'Output directory',
         callback: (value) {
           outputDir = new io.Directory(value);
  +      })
  +    ..addOption('search-dir',
  +      abbr: 's',
  +      help: 'Directory to look for mixins',
  +      defaultsTo: 'lib',
  +      callback: (value) {
  +        searchDir = new io.Directory(value);
         });
     argp.parse(args);
     if (outputDir == null || configFile == null) {
  
positive.code: 
  io.Directory outputDir;
  io.File configFile;
  
  main(List<String> args) {
    parseArgs(args);
  
negative.code:       config = mixologist.parseConfig(yaml.loadYaml(configString));
      })
      .then((_) =>
          mixologist.mix(config, new LocalFileSystem(searchDir)))
      .then((String code) {
        var outputFilePath = path.join(outputDir.path, config.output);
        new io.Directory(path.dirname(outputFilePath)).createSync(recursive: true);
  