GitLab

* Support PEP 563 for HfArgumentParser

* Fix issues for Python 3.6

* Add test for string literal annotation for HfArgumentParser

* Remove wrong comment

* Fix typo

* Improve code readability
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* Use `isinstance` to compare types to pass quality check

* Fix style
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>