Add Markdown index HTML output mode

internal/transform/transform.go

@@ -19,6 +19,12 @@ type Output struct {
 type Request struct {
 	SourceBundle  bundle.Bundle
 	SourceBackend storage.Backend
+	Markdown      MarkdownOptions
+}
+
+type MarkdownOptions struct {
+	Mode  string
+	Input string
 }
 
 type Transformer interface {