add setup.cfg to configure flake8/black/isort/mypy

setup.cfg

@@ -0,0 +1,21 @@
+[flake8]
+ignore =
+    E203 # whitespace before ':' - doesn't work well with black
+    E402 # module level import not at top of file
+    E501 # line too long - let black worry about that
+    E731 # do not assign a lambda expression, use a def
+    W503 # line break before binary operator
+exclude=
+    .eggs
+    doc
+
+[isort]
+profile = black
+skip_gitignore = true
+float_to_top = true
+default_section = THIRDPARTY
+known_first_party = datatree
+
+[mypy]
+files = datatree/**/*.py
+show_error_codes = True