[FIX] Python 3: Use chr instead of unichr in Python 3

The change in page.py is different than the normal change, because
Python 3 doesn't suffer from the problem that it might not support
charpoints above 2¹⁶.

Change-Id: Id49f6dd0aa81a8b915f20453dbb679fd840a9a80
Merge "[FIX] Python 3: Use chr instead of unichr in Python 3"