Add .style.yapf config that matches the Google internal style guide.

[Marvin182]

Unfortunately the Google internal formatting is different from PEP8
(column limit 79 -> 80 and indent width 4 -> 2, a few things around when
and how to split lines). YAPFs own style matches this but is not the default.

YAPF will automatically pick up the config when run anywhere inside the
repository.

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[codecov-commenter]

Codecov Report

Merging #384 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #384   +/-   ##
=======================================
  Coverage   78.76%   78.76%           
=======================================
  Files          34       34           
  Lines        2256     2256           
=======================================
  Hits         1777     1777           
  Misses        479      479           

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[avital]

I think this is great! A few questions:

1. Is yapf both a formatter and a linter?
2. Does it integrate with common IDEs like VSCode?
3. Is the plan to add yapf to some kind of pre-commit hook?

[Marvin182]

I think this is great! A few questions:

1. Is yapf both a formatter and a linter?
   just a formatter. It can fix some things that a linter might complain about but not all.

We probably want 3 things:

1. Linter. I don't use any.
2. Formatter that makes it a bit easier to be conform with the linter and have consistent style.
3. Type checking (internally we use pytype, I think JAX uses mypy)

2. Does it integrate with common IDEs like VSCode?
   Yes, Dan is using it with VSCode

3. Is the plan to add yapf to some kind of pre-commit hook?
   No, I think a linter and type checking would be the way to go

[avital]

Wouldn't we want to make sure all commits adhere to the same style guide? That way blame always works because you don't catch other people just reformatting a file that they are editing.