add function to convert filename to title

tests/test_util.py

@@ -0,0 +1,9 @@
+from pathlib import Path
+from zona import util
+
+
+def test_title(tmp_path: Path):
+    a = tmp_path / "my-first-post.md"
+    b = tmp_path / "Writing_emails_Post.md"
+    assert util.filename_to_title(a) == "My First Post"
+    assert util.filename_to_title(b) == "Writing Emails Post"