added black formatting

pyproject.toml

@@ -0,0 +1,11 @@
+# Example configuration for Black.
+
+# NOTE: you have to use single-quoted strings in TOML for regular expressions.
+# It's the equivalent of r-strings in Python.  Multiline strings are treated as
+# verbose regular expressions by Black.  Use [ ] to denote a significant space
+# character.
+
+[tool.black]
+line-length = 140
+target-version = ['py36', 'py37', 'py38', 'py39']
+include = '\.pyi?$'