Add formatting style search in a tox.ini file

[olekssy]

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Make yapf search search for the formatting style in the [yapf] section of a tox.ini file in either the current directory or one of its parent directories.

[Spitfire1900]

For tox.ini I would suggest passing in the --style= flag in the tox.ini over adding support for a yapf section.

Since this PR was opened out-of-the-box pyproject.toml support was added with version 0.33.0,