added nats + worker modules

worker/errors.go

@@ -0,0 +1,11 @@
+package worker
+
+import "errors"
+
+var (
+	ErrInvalidHandler     = errors.New("handler is nil")
+	ErrStreamNotFound     = errors.New("stream not found")
+	ErrConsumerNotFound   = errors.New("consumer not found")
+	ErrStreamNameRequired = errors.New("stream name required")
+	ErrSubjectRequired    = errors.New("subject required")
+)