Install Black and isort autoformatters (#3069)

* Install Black and isort

* Add config via pyproject.toml

Notably we keep the convention of 130 line length.

* Add target python version

pyproject.toml

@@ -0,0 +1,11 @@
+[tool.black]
+line_length = 130
+target_version = ["py37"]
+
+[tool.isort]
+multi_line_output = 3
+include_trailing_comma = true
+force_grid_wrap = 0
+use_parentheses = true
+combine_as_imports = true
+line_length = 130

requirements-tests-py3.txt

@@ -1,6 +1,8 @@
 git+https://github.com/python/mypy.git@master
 typed-ast>=1.0.4
+black==19.3b0
 flake8==3.6.0
 flake8-bugbear==18.8.0
 flake8-pyi==18.3.1
+isort==4.3.20
 pytype>=2019.5.15