BREAKING CHANGE: The option to define a `Standards` version has been removed. Every new rule that is added on upcoming releases is activated by default and will also create errors if triggered. The behavior of rules can be controlled by the existing `rules.exclude_filter` or `rules.warning_filter` options.
BREAKING CHANGE: The option `rules.buildin` has been renamed to `rules.builtin`.
BREAKING CHANGE: The option `rules.standards` has been renamed to `rules.dir`.
BREAKING CHANGE: The option `rules.filter` has been renamed to `rules.include_filter`.
* refactor plugin system to use a class-based approach
* disable some docstring linter errors and fix imports
* cleanup
* fix docs
* add metavars to cli arguments for better helptext
* add option to disable buildin rules
* remove print
* remove dead code
