Add initial Flake8 config

Ref #253

.flake8

@@ -0,0 +1,54 @@
+[flake8]
+
+# Don't even try to analyze these:
+exclude =
+  # No need to traverse egg files
+  *.egg,
+  # Circle CI configs
+  .circleci,
+  # No need to traverse egg info dir
+  *.egg-info,
+  # No need to traverse eggs directory
+  .eggs,
+  # No need to traverse our git directory
+  .git,
+  # GitHub configs
+  .github,
+  # Cache files of MyPy
+  .mypy_cache,
+  # Cache files of pytest
+  .pytest_cache,
+  # Temp dir of pytest-testmon
+  .tmontmp,
+  # Countless third-party libs in venvs
+  .tox,
+  # VS Code
+  .vscode,
+  # There's no value in checking cache directories
+  __pycache__,
+  # This contains builds of cheroot that we don't want to check
+  dist,
+  # Metadata of `pip wheel` cmd is autogenerated
+  pip-wheel-metadata,
+
+# Completely and unconditionally ignore the following errors:
+ignore =
+  # W503 ignored for https://github.com/PyCQA/pycodestyle/issues/498
+  W503
+
+# Let's not overcomplicate the code:
+# 29 is to facilitate the currently present maximum
+max-complexity = 29
+# max-complexity = 10  # TODO: use this once possible
+
+# Accessibility/large fonts and PEP8 friendly:
+max-line-length = 79
+
+# Allow certain violations in certain files:
+per-file-ignores =
+  # cheroot/makefile.py:125:5: C901 'If 125' is too complex (57)
+  cheroot/makefile.py: C901
+
+  # There are multiple `assert`s (S101)
+  # and subprocesses (import – S404; call – S603) in tests:
+  cheroot/test/test_*.py: S101, S404, S603

.pre-commit-config.yaml

@@ -9,9 +9,6 @@ repos:
   hooks:
   - id: trailing-whitespace
   - id: flake8
-    args:
-    # W503 ignored for https://github.com/PyCQA/pycodestyle/issues/498
-    - --ignore=W503
     additional_dependencies:
     - flake8-2020==1.0.0
   - id: check-merge-conflict