code: function parseIgnore(book) {
      if (book.isLanguageBook()) {
          return Promise.reject(new Error('Ignore files could be parsed for language books'));
      }
  
      var fs = book.getFS();
      var ignore = book.getIgnore();
  
      ignore = ignore.add(DEFAULT_IGNORES);
  
      return Promise.serie(IGNORE_FILES, function(filename) {
          return fs.readAsString(filename)
          .then(function(content) {
              ignore = ignore.add(content.toString().split(/\r?\n/));
          }, function(err) {
              return Promise();
          });
      })
  
      .then(function() {
          return book.setIgnore(ignore);
      });
  }
docs: Parse ignore files
  
  @param {Book}
  @return {Book}