feat(cmd): automatically create parent folders for output file (#36)

Co-authored-by: Michael Masson <mmasson@stingray.com>

cmd/gomarkdoc/command.go

@@ -441,7 +441,7 @@ func writeOutput(specs []*PackageSpec, opts commandOptions) error {
 				return err
 			}
 		default:
-			if err := ioutil.WriteFile(fileName, []byte(text), 0755); err != nil {
+			if err := writeFile(fileName, text); err != nil {
 				return fmt.Errorf("failed to write output file %s: %w", fileName, err)
 			}
 		}
@@ -450,6 +450,22 @@ func writeOutput(specs []*PackageSpec, opts commandOptions) error {
 	return nil
 }
 
+func writeFile(fileName string, text string) error {
+	folder := filepath.Dir(fileName)
+
+	if folder != "" {
+		if err := os.MkdirAll(folder, 0755); err != nil {
+			return fmt.Errorf("failed to create folder %s: %w", folder, err)
+		}
+	}
+
+	if err := ioutil.WriteFile(fileName, []byte(text), 0755); err != nil {
+		return fmt.Errorf("failed to write file %s: %w", fileName, err)
+	}
+
+	return nil
+}
+
 func checkFile(b *bytes.Buffer, path string) error {
 	checkErr := errors.New("output does not match current files. Did you forget to run gomarkdoc?")