Negotiate need support more format

[578559967]

Description

Negotiate function only support XML/HTML/JSON，but I need it to support YAML/Protobuf.
I think it should match the binding.Default:

gin/binding/binding.go

Lines 86 to 107 in 231ff00

	func Default(method, contentType string) Binding {
	if method == "GET" {
	return Form
	}
	switch contentType {
	case MIMEJSON:
	return JSON
	case MIMEXML, MIMEXML2:
	return XML
	case MIMEPROTOBUF:
	return ProtoBuf
	case MIMEMSGPACK, MIMEMSGPACK2:
	return MsgPack
	case MIMEYAML:
	return YAML
	case MIMEMultipartPOSTForm:
	return FormMultipart
	default: // case MIMEPOSTForm:
	return Form
	}
	}