Added

• Upgrade to and satisfy MyPy 0.910 by adding types-toml as a test dependency, and
  types-dataclasses as well if running on Python 3.6.
• Installation instructions in a Conda environment.

Fixed

• Git-related commands in the test suite now ignore the user's ~/.gitconfig.
• Now works again even if isort isn't installed
• AST verification no longer erroneously fails when using --isort
• Historical comparisons like darker --diff --revision=v1.0..v1.1 now actually
  compare the second revision and not the working tree files on disk.
• Ensure identical Black formatting on Unix and Windows by always passing Unix newlines
  to Black