Add config settings for black

It is *not* added to pre-commit yet, to allow for updating the code
piecemeal.

Author: bmerry

.flake8

@@ -1,2 +1,5 @@
 [flake8]
 max-line-length = 100
+# See https://black.readthedocs.io/en/stable/faq.html#why-are-flake8-s-e203-and-w503-violated
+extend-ignore = E203, W503
+extend-select = W504

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
 - repo: https://github.com/PyCQA/isort
-  rev: 5.10.1
+  rev: "5.10.1"
   hooks:
     - id: isort
 - repo: https://github.com/PyCQA/flake8

pyproject.toml

@@ -1,6 +1,10 @@
 [build-system]
 requires = ["setuptools", "wheel", "katversion"]
 
+[tool.black]
+line-length = 100
+target-version = ["py38"]
+
 [tool.isort]
 profile = "black"
 line_length = 100