code: function overview (req, configName, callback) {
      return get(configName).schema.statics.getOverview(req, callback);
  }
docs: Retrieve the overview DSL for a config
  @param  {Object}   req      A HTTP request object which can be used to customise the DSL
  @param  {String}   configName The name of the config
  @param  {Function} callback  A callback to return the overview DSL to
  @return {Void}