Travis: add pep8 checks

.pep8

@@ -0,0 +1,4 @@
+[pep8]
+# E265 block comment should start with '# '
+# E501 line too long (X > 79 characters)
+ignore = E265,E501

tox.ini

@@ -36,6 +36,8 @@ basepython = python2.7
 # duplicate code checking; if one of the commands fails, others will
 # continue, but tox return code will reflect previous error
 commands =
+    pip install pep8
+    pep8 setup.py acme letsencrypt letsencrypt-apache letsencrypt-nginx letsencrypt-compatibility-test letshelp-letsencrypt
     pip install -r requirements.txt -e acme -e .[dev] -e letsencrypt-apache -e letsencrypt-nginx -e letsencrypt-compatibility-test -e letshelp-letsencrypt
     pylint --rcfile=.pylintrc letsencrypt
     pylint --rcfile=.pylintrc acme/acme