Update setup.cfg (#65)

Closes #64

setup.cfg

@@ -1,13 +1,16 @@
 [flake8]
-ignore =
-    # E501: line too long
-    E501,
-    # W503: line break before binary operator
-    W503,
-max-complexity = 10
 exclude =
     .git,
     __pycache__
+max-complexity = 10
+# black docs regarding flake8: https://black.readthedocs.io/en/stable/guides/using_black_with_other_tools.html#flake8
+# black enforces an equal amount of whitespace around slice operators. It is not PEP8 compliant.
+# black and flake8 also disagree on line length
+extend-ignore = 
+    # E203: Whitespace before ':'
+    E203,
+    # E501: Line too long
+    E501,
 
 [isort]
 profile = black