Configure dev tools

.gitignore

 __pycache__/
-.mypy_cache/
\ No newline at end of file
+/.mypy_cache/
+/.venv/
\ No newline at end of file

.vscode/settings.json

+{
+  "python.pythonPath": ".venv/bin/python",
+  "python.formatting.provider": "black"
+}

requirements-dev.in

+black
+flake8
+isort
+mypy

requirements-dev.txt

+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile requirements-dev.in
+#
+appdirs==1.4.4
+    # via black
+black==20.8b1
+    # via -r requirements-dev.in
+click==7.1.2
+    # via black
+flake8==3.8.4
+    # via -r requirements-dev.in
+isort==5.7.0
+    # via -r requirements-dev.in
+mccabe==0.6.1
+    # via flake8
+mypy-extensions==0.4.3
+    # via
+    #   black
+    #   mypy
+mypy==0.812
+    # via -r requirements-dev.in
+pathspec==0.8.1
+    # via black
+pycodestyle==2.6.0
+    # via flake8
+pyflakes==2.2.0
+    # via flake8
+regex==2020.11.13
+    # via black
+toml==0.10.2
+    # via black
+typed-ast==1.4.2
+    # via
+    #   black
+    #   mypy
+typing-extensions==3.7.4.3
+    # via
+    #   black
+    #   mypy