code: function _libraryFiles(directory) {
  	return new Promise((fulfill) => {
  		const files = [];
  		klaw(directory)
  			.on('data', (item) => {
  				const relativePath = path.relative(directory, item.path);
  				files.push(relativePath);
  			})
  			.on('end', () => {
  				fulfill(files);
  			});
  	});
  }
docs: Enumerate all files relative to the root of the library
  @param {string} directory - root of the library
  @returns {Promise} - resolves to array of relative paths
  @private