Add flake8 to the testing

Author: cclauss

circle.yml

@@ -8,5 +8,7 @@ general:
       - old_master
 test:
     override:
+        - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
+        - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
         - python -m unittest discover test_replays
         - python -m unittest discover test_s2gs