code: function expandPathPlaceholders (targetPath, files, properties, yoFs) {
    trace('Expanding path placeholders');
    return files.map(file => {
      // Don't bother expanding paths without placeholders
      if (file.indexOf('__') === -1) {
        return file;
      }
      var newPath = pathFiltering.filter(file, properties);
      if (file !== newPath) {
        trace('Performing move for path expansion %s', file);
        yoFs.move(path.join(targetPath, file), path.join(targetPath, newPath));
        trace('Path expansion move completed %s', newPath);
        debug('Expanded path placeholder ', newPath);
      }
      return newPath;
    });
  }
docs: Helper goes through a list of files and expands any __placeholders__ that correspond
  with properties that have been provided.
  
  @param {!string} targetPath the root location we are generating into
  @param {!Array<string>} files a list of files relative to the target path
  @param {!Object} properties list of properties that should be considered for expansion
  @param {!Object} yoFs