Pre-commit

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- Remove backward compatibility with repositories providing metadata via
`hooks.yaml`. New repositories should provide `.pre-commit-hooks.yaml`.
Run `pre-commit autoupdate` to upgrade to the latest repositories.
- Improve golang support when running under cygwin.
- Fix crash with unstaged trailing whitespace additions while git was
configured with `apply.whitespace = error`.
- Fix crash with unstaged end-of-file crlf additions and the file's lines
ended with crlf while git was configured with `core-autocrlf = true`.

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- Add support for the `commit-msg` git hook

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- Recover from invalid python virtualenvs

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- Work around a windows-specific virtualenv bug pypa/virtualenv1062
This failure mode was introduced in 0.15.1

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- Use a more intelligent default language version for python

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- Add `types` and `exclude_types` for filtering files. These options take
an array of "tags" identified for each file. The tags are sourced from
[identify](https://github.com/chriskuehl/identify). One can list the tags
for a file by running `identify-cli filename`.
- `files` is now optional (defaulting to `''`)
- `always_run` + missing `files` also defaults to `files: ''` (previously it
defaulted to `'^$'` (this reverses e150921c).