Universalwrapper

- Introduce `output_parser` option and phase out `output_yaml`, `output_splitlines`, `output_json`, and `output_custom` (will be removed in universalwrapper 2.5)
- Introduce `parallel` option, based on `autothread.async_threaded`. This provides asynchronous commands without the use of Python's async framework.

v1
First stable release

Implementation of community feedback.

Initial release