openEpub(data, encoding) {
    return this.unarchive(data, encoding || this.settings.encoding).then(() => {
      return this.openContainer(CONTAINER_PATH);
    }).then(packagePath => {
      return this.openPackaging(packagePath);
    });
  }
Open an archived epub
@private
@param  {binary} data
@param  {string} [encoding]
@return {Promise}