Fix NewErrors() and Improve NewError()

[balcieren]

If error message's type happens interface{}, It can return multiple error strings etc.

NewErrors()

func main() {
	app := New(fiber.Config{
		ErrorHandler: func(c *fiber.Ctx, err error) error {
			code := fiber.StatusInternalServerError
			var messages interface{}

			if e, ok := err.(*fiber.Error); ok {
				code = e.Code
				messages = e.Message
			}

			return c.Status(code).JSON(fiber.Map{
				"status_code": code,
				"status_text": utils.StatusMessage(code),
				"messages":    messages,
			})
		},
	})

	app.Get("/", func(c *fiber.Ctx) error {
		return NewErrors(fiber.StatusBadRequest, "validatien error 1", "validation error 2")
	})

	app.Listen(":3000")
}

JSON is going to be

{
  "messages": [
    "validatien error 1",
    "validation error 2"
  ],
  "status_code": 400,
  "status_text": "Bad Request"
}

---

Different Example

func main() {
	app := New(fiber.Config{
		ErrorHandler: func(c *fiber.Ctx, err error) error {
			code := fiber.StatusInternalServerError
			var messages interface{}

			if e, ok := err.(*fiber.Error); ok {
				code = e.Code
				messages = e.Message
			}

			return c.Status(code).JSON(fiber.Map{
				"status_code": code,
				"status_text": utils.StatusMessage(code),
				"messages":    messages,
			})
		},
	})

	app.Get("/", func(c *fiber.Ctx) error {
		return NewErrors(StatusBadRequest,
			fiber.Map{
				"type":        "validation",
				"description": "password must be longer than 6 characters",
			},
			fiber.Map{
				"type":        "validation",
				"description": "invalid e-mail",
			})
	})

	app.Listen(":3000")
}

JSON is going to be

{
  "messages": [
    {
      "description": "password must be longer than 6 characters",
      "type": "validation"
    },
    {
      "description": "invalid e-mail",
      "type": "validation"
    }
  ],
  "status_code": 400,
  "status_text": "Bad Request"
}

[vecpeng]

It seems good but the only problem is that the type of message has been changed, which may cause backward compatibility issues.
Maybe we should wait maintainers' review.
@ReneWerner87 @efectn @hi019 what do you think?

[balcieren]

It seems good but the only problem is that the type of message has been changed, which may cause backward compatibility issues. Maybe we should wait maintainers' review. @ReneWerner87 @efectn @hi019 what do you think?

Echo also uses interface{} for message

[balcieren]

@ReneWerner87 I think it is not big update and all checks have passed. What do you think ?

[ReneWerner87]

I look at it today, had the week other tasks to do

[welcome]

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[balcieren]

@ReneWerner87 I have updated doc, PR

[ReneWerner87]

Thx