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