code: function parsePatterns(options) {
    return readFileTree(
      options.src.patterns,
      options.keys.patterns,
      options
    ).then(patternObj => {
      return Promise.all(buildCollections(patternObj, options)).then(
        () => patternObj,
        error => DrizzleError.error(error, options.debug)
      );
    });
  }
docs: Parse pattern files and then flesh out individual pattern objects and
  build collection data.
  
  @param {Object} options
  @return {Promise} resolving to pattern/collection data