YAPF, take 3 (#2098)

* Use pep8 style

The original style file is actually just pep8 style, but with everything
spelled out. It's easier to use the `based_on_style` feature. Any overrides are
clearer that way.

* Improve yapf script

1. Do formatting in parallel
2. Lint RLlib
3. Use .style.yapf file

* Pull out expressions into variables

* Don't format rllib

* Don't allow splits in dicts

* Apply yapf

* Disallow single line if-statements

* Use arithmetic comparison

* Simplify checking for changed files

* Pull out expr into var

python/setup.py

@@ -52,8 +52,9 @@ else:
 optional_ray_files += ray_autoscaler_files
 
 extras = {
-    "rllib":
-    ["tensorflow", "pyyaml", "gym[atari]", "opencv-python", "lz4", "scipy"]
+    "rllib": [
+        "tensorflow", "pyyaml", "gym[atari]", "opencv-python", "lz4", "scipy"
+    ]
 }