code: function addEngine (helpers, hbs, hbsOptions) {
    hbs.logger.level = 0
    // Provide the engine as last parameter to all helpers in order to
    // enable things like calling partials from a helper.
    return _.mapValues(helpers, (helper) =>
      function wrappedHelper () {
        var options = arguments[arguments.length - 1]
        options.customize = {
          engine: hbs,
          config: hbsOptions,
          targetFile: options.data.root.__customize_target_file__
        }
        return helper.apply(this, arguments)
      }
    )
  }
docs: Wraps helpers with a function that provides
  and object {engine, config} as additional parameter
  @param {object<function>} helpers the helpers object
  @param {Handlebars} hbs the current handlebars engine
  @param {object} hbsOptions the options of the Handlebars engine
  @return {object<function>} the wrapped helpers
  @access private