Add python 3.5 testing environment

Python 3.5 is not yet fully integrated in travis. Include
workaround to enable it for now.

.travis.yml

@@ -7,6 +7,11 @@ env:
   - TOX_ENV=py27
   - TOX_ENV=py33
   - TOX_ENV=py34
+matrix:
+  include:
+    - python: 3.5
+      env:
+      - TOX_ENV=py35
 addons:
   apt_packages:
     - pandoc

tox.ini

@@ -1,11 +1,12 @@
 [tox]
-envlist = py{27,33,34},docs,flake8
+envlist = py{27,33,34,35},docs,flake8
 
 [testenv]
 basepython =
     py27: python2.7
     py33: python3.3
     py34: python3.4
+    py35: python3.5
 passenv = *
 usedevelop=True
 deps =