Keewis Blackdoc Versions Save

Bug fixes:

• fix formatting empty doctest lines
• don't change the triple quote style of nested docstrings

New features:

• add support for the testcode rst directives
• read settings from a configuration file
• add the --force-exclude option

Bugfix release:

• keep compatibility with black version 20.8b1

Fixed bugs / new features:

• always return a non-zero error code if there was an error
• add a pre-commit hook configuration

The initial release