server.go
func (ctx *RequestCtx) SuccessString(contentType, body string) {
	ctx.SetContentType(contentType)
	ctx.SetBodyString(body)
}
func (ctx *RequestCtx) SuccessString(contentType, body string) {
	ctx.SetContentType(contentType)
	ctx.SetBodyString(body)
}
// SuccessString sets response Content-Type and body to the given values.