Add notes on 1.6.0, and mark 1.5.0 as complete

Author: dominicrodger

docs/changelog.rst

@@ -1,9 +1,17 @@
 Changelog
 =========
 
-1.5.0 (pending)
+1.6.0 (Pending)
 ---------------
 
+* Fixes for Python 3 (:issue:`105`);
+* Support for Django 2.0 (:issue:`109`, :issue:`110`);
+* Switch back a couple of instances of ``DeserializationError`` to
+``ValidationError`` (:issue:`111`).
+
+1.5.0
+-----
+
 * Add Slovakian translations (:issue:`98`);
 * Add support for events occurring at a fixed point before the
   end of the month - e.g. the second last Tuesday before the end of