Perform McCabe complexity checks as part of CI

.travis.yml

@@ -13,9 +13,12 @@ install:
   - "pip install .[test]"
   - "pip install pylint"
   - "pip install codecov"
+  - "pip install flake8"
+  - "pip install mccabe"
 script:
   - "green -vvr"
   - "python -m pylint --errors-only topydo test"
+  - "flake8 topydo test"
 # Cache Dependencies
 after_script:
   - codecov

setup.cfg

@@ -0,0 +1,3 @@
+[flake8]
+select = C901
+max-complexity = 10