Update CHANGELOG for 7.20.

CHANGELOG

@@ -1,3 +1,22 @@
+Quake II 7.10 to 7.20:
+- Add the soft renderer back. This feature is considered experimental.
+  The porting of the old soft renderer code to SDL and it's cleanup
+  were done by Denis Pauk.
+- Rename several cvars to be consistent with other Quake II source
+  ports. The configuration file will be converted at the first start,
+  when an old cvar name is used a message is printed.
+- Make the client unicode compatible. Yamagi Quake II can now be 
+  installed into pathes with unicode characters in it. On Windows the
+  user name of the current account may contain unicode characters.
+  As a side effect the game can run on ReFS volumes. While '+set
+  basedir' is still supported, the unicode compatible '-datadir'
+  should be used.
+- Another round of timing fixes. The game is now capable of holding
+  the requestes or vsync framerate even on slow machines and with
+  problematic GL drivers.
+- Fix server side mod handling, their configs are now saved to the
+  correct directories and the configs are reexeced at mod startup.
+
 Quake II 7.02 to 7.10:
 - Joystick support including haptic feedback. This fantastic work was
   done by Denis Pauk. The dirty work is done by SDL, how good or bad