add .md suffix implicit for files

fstree.go

@@ -42,7 +42,11 @@ type FsNode struct {
 }
 
 func (n *FsNode) FileName() string {
-	return filepath.Base(n.path)
+	name := filepath.Base(n.path)
+	if n.nodeType == FileNode {
+		return strings.TrimSuffix(name, ".md")
+	}
+	return name
 }
 
 // ================== messages ===================
@@ -425,6 +429,10 @@ func (t *FsTree) CreateNode(folder *FsNode, name string, nodeType FsNodeType) er
 		return errors.New("node name cannot be empty")
 	}
 
+	if nodeType == FileNode && !strings.HasSuffix(name, ".md") {
+		name += ".md"
+	}
+
 	path := filepath.Join(folder.path, name)
 	// materialise it first
 	switch nodeType {