code: func (c *Client) GetCategories() (resp GetCategoriesResponse, err error) {
  	jsonBody, _ := json.Marshal(nil)
  
  	err = c.Call("/categories/get", jsonBody, &resp)
  	return resp, err
  }
docs: // GetCategories returns information for all categories.
  // See https://plaid.com/docs/api/#category-overview.