Add flake8 to tox

Author: sjagoe

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = cp{26,27,33,34,35},pp{2,3},cp26-win
+envlist = cp{26,27,33,34,35},pp{2,3},cp26-win,flake8
 minversion=2.7
 
 [testenv]
@@ -52,3 +52,16 @@ commands =
 # The tox environment for cp33 needs a specific set of base
 # dependencies for wheel, pip and setuptools
 deps = -rcp33-tox-requirements.txt
+
+[testenv:flake8]
+basepython = python3
+skip_install = true
+deps = flake8
+commands = flake8
+
+[flake8]
+exclude =
+    .tox,
+    .git,
+    __pycache__,
+    docs/source/conf.py