Added

• -f / --flynt option for converting old-style format strings to f-strings as
  supported in Python 3.6+.
• Make unit tests compatible with pytest --log-cli-level==DEBUG.
  Doctests are still incompatible due to
  pytest#5908 <https://github.com/pytest-dev/pytest/issues/5908>_.
• Black's target-version = configuration file option and -t /
  --target-version command line option
• In README.rst, link to GitHub searches which find public repositories that
  use Darker.
• Linters are now run twice: once for rev1 to get a baseline, and another time for
  rev2 to get the current situation. Old linter messages which fall on unmodified
  lines are hidden, so effectively the user gets new linter messages introduced by
  latest changes, as well as persistent linter messages on modified lines.
• --stdin-filename=PATH now allows reading contents of a single file from standard
  input. This also makes :STDIN:, a new magic value, the default rev2 for
  --revision.
• Add configuration for darglint and flake8-docstrings, preparing for enabling
  those linters in CI builds.

Fixed

• Compatibility of highlighting unit tests with Pygments 2.14.0.
• In the CI test workflow, don't use environment variables to add a Black version
  constraint to the pip command. This fixes the Windows builds.
• Pass Git errors to stderr correctly both in raw and encoded subprocess output mode.
• Add a work-around for cleaning up temporary directories. Needed for Python 3.7 on
  Windows.
• Split and join command lines using shlex from the Python standard library. This
  deals with quoting correctly.
• Configure coverage to use relative paths in the Darker repository. This enables
  use of cov_to_lint.py
• Satisfy Pylint's use-dict-literal check in Darker's code base.
• Use !r to quote values in format strings as suggested by recent Flake8 versions.