client.go
func (c *Client) Endpoint(params ...string) string {
	if c.v != "" {
		return fmt.Sprintf("%s/%s/%s", c.addr, c.v, strings.Join(params, "/"))
	}
	return fmt.Sprintf("%s/%s", c.addr, strings.Join(params, "/"))
}
func (c *Client) Endpoint(params ...string) string {
	if c.v != "" {
		return fmt.Sprintf("%s/%s/%s", c.addr, c.v, strings.Join(params, "/"))
	}
	return fmt.Sprintf("%s/%s", c.addr, strings.Join(params, "/"))
}
// Endpoint returns a URL constructed from parts and version appended, e.g.
//
// c.Endpoint("user", "john") // returns "/v1/users/john"
//