List Python 3.3 as supported. Fixes #513.

NEWS

@@ -1,5 +1,9 @@
 0.17.3	UNRELEASED
 
+ PLATFORM SUPPORT
+
+  * List Python 3.3 as supported. (Jelmer Vernooij, #513)
+
 0.17.2	2017-03-19
 
  BUG FIXES

README.md

@@ -47,4 +47,4 @@ mailing lists.
 Supported versions of Python
 ----------------------------
 
-At the moment, Dulwich supports (and is tested on) CPython 2.7, 3.4, 3.5 and Pypy.
+At the moment, Dulwich supports (and is tested on) CPython 2.7, 3.3, 3.4, 3.5, 3.6 and Pypy.

setup.py

@@ -91,8 +91,10 @@ setup(name='dulwich',
           'Development Status :: 4 - Beta',
           'License :: OSI Approved :: Apache Software License',
           'Programming Language :: Python :: 2.7',
+          'Programming Language :: Python :: 3.3',
           'Programming Language :: Python :: 3.4',
           'Programming Language :: Python :: 3.5',
+          'Programming Language :: Python :: 3.6',
           'Programming Language :: Python :: Implementation :: CPython',
           'Programming Language :: Python :: Implementation :: PyPy',
           'Operating System :: POSIX',