Prepare v0.6 release.

CHANGES.rst

 Changes
 =======
 
-0.6.dev0 (unreleased)
----------------------
+0.6 (2015-12-15)
+----------------
 
 - Officially support Pyhthon 3.5.
 - Tests do not depend on `pytest-cov`, `pytest-xdist` anymore.

setup.py

@@ -44,7 +44,7 @@ docs_require = [
 
 setup(
     name="diceware",
-    version="0.6.dev0",
+    version="0.6",
     author="Uli Fouquet",
     author_email="uli@gnufix.de",
     description=(