Openapi-python-client

- Improve handling of optional properties in generated `to_dict` function for models
- Add PEP 561 marker file (py.typed) to generated packages

- Fix mypy issue in generated models `from_dict` with datetime or reference properties
- Generated clients now raise an `ApiResponseError` if they receive a response that was not declared
- Stop including optional query parameters when value is set to None
- Added an `update` command to update a previously generated client
- Added click-completion for installable tab completion in most shells

- Initial Release