improve highlighting

highlight.py

@@ -0,0 +1,12 @@
+from typing import Optional
+
+from line import Line
+from highlighted_range import HighlightedRange
+
+
+class Highlight:
+    def __init__(self):
+        pass
+
+    def compute_highlight(self, line: Line) -> Optional[HighlightedRange]:
+        return None