Put project modules under pkg directory

pkg/cgnolink/errors/errors.go

@@ -0,0 +1,29 @@
+package errors
+
+type UnknownError struct {
+	Err error
+}
+
+func (err UnknownError) Error() string {
+	return err.Err.Error()
+}
+
+func (err UnknownError) Unwrap() error {
+	return err.Err
+}
+
+type NotFoundError struct {
+	Message string
+}
+
+func (err NotFoundError) Error() string {
+	return err.Message
+}
+
+type AlreadyExistsError struct {
+	Message string
+}
+
+func (err AlreadyExistsError) Error() string {
+	return err.Message
+}