Automate Flake8 check in the CI.

dev-requirements.txt

@@ -2,3 +2,4 @@ zest.releaser
 tox
 pytest
 Flask-Testing
+Flake8

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py35,py34,py27,docs
+envlist = py35,py34,py27,docs,lint
 skip_missing_interpreters = True
 
 [testenv]
@@ -17,3 +17,12 @@ install_command = pip install --pre {opts} {packages}
 commands = sphinx-build -a -n -b html -d docs/_build/doctrees docs docs/_build/html
 deps =
     -rdocs/requirements.txt
+
+[testenv:lint]
+commands = flake8 ihatemoney
+deps =
+    -rdev-requirements.txt
+
+[flake8]
+exclude = migrations
+max_line_length = 100