func Subscribe(topic string, h Handler) (Subscriber, error) {
	return DefaultBroker.Subscribe(topic, h)
}
Subscribe to a topic
package broker
var (
	DefaultBroker Broker
)
type Broker interface {
	Init(...Option) error
	Options() Options
	Address() string
	Connect() error
	Disconnect() error
	Publish(topic string, m *Message, opts ...PublishOption) error
	Subscribe(topic string, h Handler, opts ...SubscribeOption) (Subscriber, error)
	String() string
}
type Handler func(*Message) error
type ErrorHandler func(*Message, error)
type Message struct {
	Header map[string]string
	Body   []byte
}
type Subscriber interface {
	Options() SubscribeOptions
	Topic() string
	Unsubscribe() error
}
func Publish(topic string, m *Message) error {
	return DefaultBroker.Publish(topic, m)
}